Difference between revisions of "OPS435 Python3 Lab 8"

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<font color='red'><u>'''This lab is currently being reviewed. The final version will be ready by November 11, 2019'''</u></font>
 
 
= LAB OBJECTIVES =
 
= LAB OBJECTIVES =
 +
:0. Review SSH setup and remote shell execution
 +
:1. Explore the Fabric Python library and its command line tool "fab".
 +
:2. Create Fabric scripts utilizing Fabric's API to define tasks for the '''fab''' command.
 +
:3. Use the '''fab''' command to execute fabric script to perform pre-defined tasks on remote Linux machines.
  
−
:Completing this course will give you the prerequisites for getting into the DevOps field. A DevOps professional is a system/network administrator with programming skills. As an introduction to that field, we will look at '''Fabric''' in this lab. Using Fabric you can automate deploying software, monitoring, and updating many systems at the same time.
+
== Overview ==
 +
: Fabric is a Python library and command-line tool for streamlining the use of SSH for application deployment or system administration tasks. It has two major components:
 +
:# a command-line interface program called "fab" that lets you execute arbitrary Python functions
 +
:# a set of Python APIs that you can use and call in your Python functions to make executing shell commands over SSH much easier.  
 +
: We are going use the Fabric API and its '''fab''' command to define and execute Python functions (or tasks), to automate interactions with remote Linux machines in this lab.  
  
 
== REFERENCE ==
 
== REFERENCE ==
−
:These links are helpful for learning more about Fabric's features:
+
:1. These links are helpful for learning more about Fabric's features:
  
 
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| style="border: 2px solid black;" | Category  
 
| style="border: 2px solid black;" | Category  
 
| style="border: 2px solid black;" | Resource Link
 
| style="border: 2px solid black;" | Resource Link
−
 
−
|-  style="background-color:white;border:none;"
 
−
| style="border: 2px solid black;" valign="top"| 
 
−
:Official '''Fabric''' website
 
−
| style="border: 2px solid black;" valign="top"| 
 
−
:[http://www.fabfile.org/]
 
  
 
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:[https://www.digitalocean.com/community/tutorials/how-to-use-fabric-to-automate-administration-tasks-and-deployments]
 
:[https://www.digitalocean.com/community/tutorials/how-to-use-fabric-to-automate-administration-tasks-and-deployments]
  
 +
|-  style="background-color:white;border:none;"
 +
| style="border: 2px solid black;" valign="top"| 
 +
:Official '''Fabric''' website
 +
| style="border: 2px solid black;" valign="top"| 
 +
:[http://www.fabfile.org/]
 
|}
 
|}
 +
: <font color='blue'>Please note that the version of Fabric installed on matrix.senecacollege.ca for this lab is 1.14 and it supports only Python version 2.</font> The Fabric script files we are going to create in this lab have to meet Python version 2.x requirements. (e.g. print is a keyword, not a built-in function in Python 2.x)
 +
:2. You should have some experience on the following topics in OPS235 and or OPS335. Please review them to prepare for the activities in this lab:
 +
:* create and configure a regular user on a Linux system.
 +
:* configure and manage sudo privilege for a regular user
 +
:* Configure sudoers using the visudo command
 +
:* using the yum command to install, remove, and update rpm packages
 +
:* Retrieve current firewall setting using the iptables -L -n -v command
  
−
== Topics to be reviewed ==
+
= INVESTIGATION 1: The Fabric Environment  =
−
: sudo and sudoers
 
−
:* man page on sudo
 
−
:* the sudoers file: /etc/sudoers
 
  
−
= INVESTIGATION 1: Extra VM Setup =
+
: The Fabric environment consists of the following components:
 +
 
 +
:# Controller workstation - the machine that has the Fabric package installed and runs the "fab" command
 +
:## the Fabric Python Library - the fabric package (already installed on matrix)
 +
:## the Fabric API - fabric.api
 +
:## the Fabric command - '''fab''': run Fabric script, name of the script is default to fabfile.py in the current working directory unless specified otherwise with the '-f' option.
 +
:## Fabric script: contains fabric environment object value and Python functions (or tasks) to be executed by the '''fab''' command.
 +
:# Remote machine: the target machine on which one or more Fabric tasks will be executed.
 +
:## running the ssh server daemon
 +
:## use public key (or password based) authentication for ssh connection
  
−
: In order to experience Fabric's features in a realistic way, we're going to set up several virtual machines. To begin with they are all going to have the same configuration. Please make sure that each VM has direct network connect with other VMs you wish to control and configure.
+
== PART 1 - Configure and test your controller workstation ==
 +
: In this lab you will use your login account on matrix.senecacollege.ca as your Fabric controller workstation.  
  
−
== PART 1 - Set up your controller ==
+
: The Fabric package version 1.14.0 has already been installed on matrix.senecacollege.ca. You should have access to the '''fab''' command on matrix. Login to matrix.senecacollege.ca and run the following command to confirm the version of the fabric package:<source lang='bash'>
 +
fab --version
 +
</source>
 +
: Type the following command to get the command line options of the fab command:<source lang='bash'>
 +
fab --help
 +
</source>
 +
:You should get something similar to the following:<source lang="bash">
 +
Usage: fab [options] <command>[:arg1,arg2=val2,host=foo,hosts='h1;h2',...] ...
  
−
: In this lab you will use your existing vm '''centos7''' as a workstation to control other VMs which we'll call workers.
+
Options:
 +
  -h, --help            show this help message and exit
 +
  -d NAME, --display=NAME
 +
                        print detailed info about command NAME
 +
  -F FORMAT, --list-format=FORMAT
 +
                        formats --list, choices: short, normal, nested
 +
  -I, --initial-password-prompt
 +
                        Force password prompt up-front
 +
  --initial-sudo-password-prompt
 +
                        Force sudo password prompt up-front
 +
  -l, --list            print list of possible commands and exit
 +
  --set=KEY=VALUE,...  comma separated KEY=VALUE pairs to set Fab env vars
 +
  --shortlist          alias for -F short --list
 +
  -V, --version        show program's version number and exit
 +
  -a, --no_agent        don't use the running SSH agent
 +
  -A, --forward-agent  forward local agent to remote end
 +
  --abort-on-prompts    abort instead of prompting (for password, host, etc)
 +
  -c PATH, --config=PATH
 +
                        specify location of config file to use
 +
  --colorize-errors    Color error output
 +
  -D, --disable-known-hosts
 +
                        do not load user known_hosts file
 +
  -e, --eagerly-disconnect
 +
                        disconnect from hosts as soon as possible
 +
  -f PATH, --fabfile=PATH
 +
                        python module file to import, e.g. '../other.py'
 +
  -g HOST, --gateway=HOST
 +
                        gateway host to connect through
 +
  --gss-auth            Use GSS-API authentication
 +
  --gss-deleg          Delegate GSS-API client credentials or not
 +
  --gss-kex            Perform GSS-API Key Exchange and user authentication
 +
  --hide=LEVELS        comma-separated list of output levels to hide
 +
  -H HOSTS, --hosts=HOSTS
 +
                        comma-separated list of hosts to operate on
 +
  -i PATH              path to SSH private key file. May be repeated.
 +
  -k, --no-keys        don't load private key files from ~/.ssh/
 +
  --keepalive=N        enables a keepalive every N seconds
 +
  --linewise            print line-by-line instead of byte-by-byte
 +
  -n M, --connection-attempts=M
 +
                        make M attempts to connect before giving up
 +
  --no-pty              do not use pseudo-terminal in run/sudo
 +
  -p PASSWORD, --password=PASSWORD
 +
                        password for use with authentication and/or sudo
 +
  -P, --parallel        default to parallel execution method
 +
  --port=PORT          SSH connection port
 +
  -r, --reject-unknown-hosts
 +
                        reject unknown hosts
 +
  --sudo-password=SUDO_PASSWORD
 +
                        password for use with sudo only
 +
  --system-known-hosts=SYSTEM_KNOWN_HOSTS
 +
                        load system known_hosts file before reading user
 +
                        known_hosts
 +
  -R ROLES, --roles=ROLES
 +
                        comma-separated list of roles to operate on
 +
  -s SHELL, --shell=SHELL
 +
                        specify a new shell, defaults to '/bin/bash -l -c'
 +
  --show=LEVELS        comma-separated list of output levels to show
 +
  --skip-bad-hosts      skip over hosts that can't be reached
 +
  --skip-unknown-tasks  skip over unknown tasks
 +
  --ssh-config-path=PATH
 +
                        Path to SSH config file
 +
  -t N, --timeout=N    set connection timeout to N seconds
 +
  -T N, --command-timeout=N
 +
                        set remote command timeout to N seconds
 +
  -u USER, --user=USER  username to use when connecting to remote hosts
 +
  -w, --warn-only      warn, instead of abort, when commands fail
 +
  -x HOSTS, --exclude-hosts=HOSTS
 +
                        comma-separated list of hosts to exclude
 +
  -z INT, --pool-size=INT
 +
                        number of concurrent processes to use in parallel mode
 +
</source>
 +
<font color='green'><b>Please note and study the following command-line options as they will be used in some of the activities in this lab:
 +
:# -H,
 +
:# -f,
 +
:# -i,
 +
:# -l,
 +
:# --port
 +
:# --user
 +
:# --initial-sudo-password-prompt
 +
</b></font>
  
−
: Install '''fabric''' using yum. Once it's installed you should have a '''fab''' command available.
+
== PART 2: Connect to VM in myvmlab.senecacollege.ca ==
 +
: You should have received an email from ITS containing the following information:
 +
:* account name: (usually 'student')
 +
:* password: (let's assume it is 'P@ssw0rd' for the following instruction in this lab)
 +
:* port number for SSH access via myvmlab.senecacollege.ca (e.g. 7200)
 +
: This VM will be used as the remote Linux machine in our Fabric environment. Login to matrix and try the following SSH command to test the connectivity between matrix and your assignment VM:
 +
<pre>
 +
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca
 +
student@myvmlab.senecacollege.ca's password:
 +
Last login: Fri Jul  3 11:06:24 2020 from mtrx-node05pd.dcm.senecacollege.ca
 +
</pre>
 +
: Once you are on your VM, try the following commands: hostname, id, and df, and record the results for later comparison with the results of other commands:<source lang='bash'>
 +
[student@centos7 ~]$ hostname
 +
centos7
 +
[student@centos7 ~]$ id
 +
uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
 +
[student@centos7 ~]$ df
 +
Filesystem              1K-blocks    Used Available Use% Mounted on
 +
devtmpfs                  878260      0    878260  0% /dev
 +
tmpfs                      889792      0    889792  0% /dev/shm
 +
tmpfs                      889792    9492    880300  2% /run
 +
tmpfs                      889792      0    889792  0% /sys/fs/cgroup
 +
/dev/mapper/centos-root  38680112 1745524  36934588  5% /
 +
/dev/sda2                1038336  331228    707108  32% /boot
 +
/dev/sda1                  204580  11296    193284  6% /boot/efi
 +
/dev/mapper/centos-home  18880512  33160  18847352  1% /home
 +
tmpfs                      177960      0    177960  0% /run/user/1002
 +
</source>
 +
:Logout from your VM and get back to matrix.
 +
:The previous SSH command when executed successfully, created a login shell on the remote machine. If the previous SSH command is followed by a specific bash command, it will be executed on the remote host instead of creating a login shell. Consider the following:<source lang='bash'>
 +
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca 'hostname;id;df'
 +
student@myvmlab.senecacollege.ca's password:
 +
centos7
 +
uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
 +
Filesystem              1K-blocks    Used Available Use% Mounted on
 +
devtmpfs                  878260      0    878260  0% /dev
 +
tmpfs                      889792      0    889792  0% /dev/shm
 +
tmpfs                      889792    9492    880300  2% /run
 +
tmpfs                      889792      0    889792  0% /sys/fs/cgroup
 +
/dev/mapper/centos-root  38680112 1745608  36934504  5% /
 +
/dev/sda2                1038336  331228    707108  32% /boot
 +
/dev/sda1                  204580  11296    193284  6% /boot/efi
 +
/dev/mapper/centos-home  18880512  33160  18847352  1% /home
 +
tmpfs                      177960      0    177960  0% /run/user/1002
 +
</source>
 +
:The three shell commands: hostname, id, and df were executed sequentially. Compare the outputs above with the previous results when executing the corresponding commands in the login shell.
 +
:Please note that you were asked to provide the user's password for every SSH connection.
  
−
== PART 2 - Create master Worker image ==
+
==PART 3: Set up SSH login with public key authentication ==
 +
: In order for your controller workstation to automate tasks execution on your VM, you need to configure your VM  to SSH public key authentication instead of password authentication. You've done this in both OPS235 and OPS335, and here is a summary on how to do it between your account on matrix and your VM:
  
−
: Create a new virtual machine, and allocate for it 1GB of RAM and 8GB of disk space. Install a Basic Web Server configuration of CentOS in that VM using the same CentOS .iso file you used for your first machine in this course.
+
: Create a new SSH key pair (one private, and one public) under your account on matrix.senecacollege.ca.
 +
: Once you have both keys, you can use the '''ssh-copy-id''' command to copy your public key to the student account on your VM, replace the port number with the correct value for your VM:<source lang='bash'>
 +
ssh-copy-id -i ~/.ssh/id_rsa.pub -p 7200 student@myvmlab.senecacollege.ca
 +
</source>
 +
: The above command should add the contents of your pub key to ~/.ssh/authorized_keys under your student account on your VM.
 +
: Verify and confirm that your account on matrix can SSH to your VM as 'student' without prompting for a password:<source lang='bash'>
 +
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca
 +
Last login: Fri Jul  3 12:46:19 2020 from mtrx-node05pd.dcm.senecacollege.ca
 +
[student@centos7 ~]$ exit
 +
logout
 +
Connection to myvmlab.senecacollege.ca closed.
  
−
: Make sure that:
+
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca 'date;hostname;id'
−
:* The hostname of the system is '''worker1'''.
+
Fri Jul  3 12:55:22 EDT 2020
−
:* It has a static IP address appropriate for your virtual network.
+
centos7
−
:* Create a regular user using your Seneca email name as the user name.
+
uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
−
:* Add this new regular user to the '''wheel''' group using the following command:<source lang="bash">
+
[raymond.chan@mtrx-node05pd lab8]$
−
    usermod -a -G wheel [seneca_id]
+
</source>
−
</source>This will allow the user to run the '''sudo'''  command.
+
: If you got similar result as above, you have successfully configure your controller workstation and your VM to use public key authentication.
−
:* After installation ensure that you can access '''worker1''' from your main vm using the static IP address you've assigned to it.
 
  
−
=== Set up SSH key login ===
+
=INVESTIGATION 2 - Running the fab command in ad-hoc mode =
−
: In order for an automated system to be able to connect to your VM and administer it - you will need to be able to connect to it using SSH keys. You've done this in both OPS235 and OPS335.
+
: The fab command relies on SSH to make the connection to the remote machine before executing the intended commands. The fab command can run in ad-hoc mode:<source lang='bash'>
 +
fab [options] -- [shell commands]
 +
</source>
 +
: When running the fab command in ad-hoc mode, it is very similar to running the SSH with commands attached at the end.
 +
== PART 1: running non-privileged shell commands on remote machines ==
 +
: In the following example, we use the '''fab''' to execute the "date", "hostname", and "id" command remotely on our VM. Try the following ad-hoc fab commands and record their results for later use, replace the port number with the correct value for your VM:<source lang='bash'>
 +
[raymond.chan@mtrx-node05pd lab8]$ fab --host=myvmlab.senecacollege.ca --port=7200 --user=student -- 'date;hostname;id'
 +
[myvmlab.senecacollege.ca] Executing task '<remainder>'
 +
[myvmlab.senecacollege.ca] run: date;hostname;id
 +
[myvmlab.senecacollege.ca] out: Fri Jul  3 13:05:39 EDT 2020
 +
[myvmlab.senecacollege.ca] out: centos7
 +
[myvmlab.senecacollege.ca] out: uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
 +
[myvmlab.senecacollege.ca] out:
  
−
: Create a new SSH key on your main VM with your regular user. Please do not use root. Then set things up so that your regular user on your '''controller VM''' can SSH to the worker VM as (the same regular user) without putting in a password.
 
  
−
== PART 3 - Clone the Workers ==
+
Done.
−
: We're only simulating the real world where you'd have hundreds of VMs in one or more clouds, but you can just imagine that the VMs you're creating on your computer are actually being created on an Amazon or Microsoft server.
+
Disconnecting from myvmlab.senecacollege.ca:7200... done.
 +
[raymond.chan@mtrx-node05pd lab8]$
 +
</source>
 +
: Note that there is no password prompting if you complete part 3 successfully, otherwise, the SSH server daemon on your VM will prompt you for a password. The output from the fab's ad-hoc mode is not much different from the SSH command with shell command attached at the end, however, please note that the additional information on the output from the fab command can be very useful for record keeping purpose - what has been done and whether the commands had been carried out successfully or not.
  
−
: '''** Optional **''' Make four clones of the master worker image you've just created. Then make sure that each of them has a unique IP address. That's all you're required to change manually. All the other configuration on the workers (inlcuding the hostnames) will be set by Fabric. Normally you would have some kind of automation doing all this cloning and IP address assignment as well, but we don't have time for that this semester.
+
== PART 2: running privileged commands on remote machines ==
 +
: We say that running an ad-hoc fab command is very similar to the SSH command with shell commands attached at the end. Let's try both with privileged commands, like the "yum" command.
  
−
: Make snapshots of all your workers so that you can easily restore them to the original state after you modify them.
+
=== Run the "yum" command on remote machine with SSH ===
−
 
+
: By default, your VM doesn't have the "tree" rpm package installed. You can verify this with the following SSH command (remember to replace the port number with the correct value for your VM):<source lang='bash'>
−
= INVESTIGATION 2: Fabric practice =
+
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca "yum list tree"
−
: We will start with some basics. Fabric runs python programs on the controller and the workers. You create an "instruction" file on your controller, and execute it on the controller using the '''fab''' program. When you do that - you specify which workers you want your instructions to be executed on.
+
Loaded plugins: fastestmirror
−
 
+
Loading mirror speeds from cached hostfile
−
: The instructions are stored in a python file. Let's start with a simple one named '''fabfile.py''' (the default filename for fab):
+
* base: centos.mirror.colo-serv.net
−
 
+
* extras: centos.mirror.colo-serv.net
−
== PART 1: Simplest example ==
+
* updates: centos.mirror.ca.planethoster.net
−
: <source lang="python">from fabric.api import *
+
Available Packages
−
 
+
tree.x86_64                          1.6.0-10.el7                          base
−
# Will get the hostname of this worker:
+
[raymond.chan@mtrx-node05pd lab8]$
−
def getHostname():
+
</source>
−
    name = run("hostname")
+
: Please note that the tree package is "Available", but not yet installed.
−
    print(name)
+
: Let't try to install the "tree" package with the shell command "yum install tree -y":<source lang='bash'>
 +
[raymond.chan@mtrx-node05pd lab8]$ ssh -p student@myvmlab.senecacollege.ca "yum install tree -y"
 +
Loaded plugins: fastestmirror
 +
You need to be root to perform this command.
 
</source>
 
</source>
 +
: Using the "yum" command to query rpm package doesn't need special privilege, however, it does when you try to install or remove rpm packages.
 +
: Your "student" account on your VM was configured to allow you to run the "sudo" command to perform software management using the "yum" command. Let's login to your VM and try the following "sudo" command to install and then remove the "tree" rpm package:<source lang='bash'>
 +
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca
 +
Last login: Fri Jul  3 16:51:07 2020 from mtrx-node05pd.dcm.senecacollege.ca
 +
[student@centos7 ~]$ sudo yum install tree -y
 +
[sudo] password for student:
 +
Loaded plugins: fastestmirror
 +
Loading mirror speeds from cached hostfile
 +
* base: less.cogeco.net
 +
* extras: centos.mirror.colo-serv.net
 +
* updates: mirror.calgah.com
 +
Resolving Dependencies
 +
--> Running transaction check
 +
---> Package tree.x86_64 0:1.6.0-10.el7 will be installed
 +
--> Finished Dependency Resolution
  
−
:All this will do is get the hostname of the worker and print it (on the controller). We run it on the controller like this:
+
Dependencies Resolved
  
−
: <source lang="bash">fab --fabfile=fabfile.py -H 192.168.56.11 getHostname</source>
+
========================================================================================================================
 +
Package                  Arch                      Version                            Repository                Size
 +
========================================================================================================================
 +
Installing:
 +
tree                    x86_64                    1.6.0-10.el7                        base                      46 k
  
−
: In the command above we're using the fab program to read the file fabfile.py and execute the getHostname function on the worker 192.168.56.11. Note that the IP address of your first worker will likely be different.
+
Transaction Summary
 +
========================================================================================================================
 +
Install  1 Package
  
−
: If you did all the setup right and you try to execute the command above - you will get a password prompt. That shouldn't happen, the point is for everything to be automated, and that's why you've set up SSH keys. To fix it, add the following to your fab file:
+
Total download size: 46 k
 +
Installed size: 87 k
 +
Downloading packages:
 +
tree-1.6.0-10.el7.x86_64.rpm                                                                    |  46 kB  00:00:00
 +
Running transaction check
 +
Running transaction test
 +
Transaction test succeeded
 +
Running transaction
 +
  Installing : tree-1.6.0-10.el7.x86_64                                                                            1/1
 +
  Verifying  : tree-1.6.0-10.el7.x86_64                                                                            1/1
  
−
:<source lang="python">env.user = 'root'</source>
+
Installed:
 +
  tree.x86_64 0:1.6.0-10.el7
  
−
:That should have worked, and you'd get output like this:
+
Complete!
 +
[student@centos7 ~]$
 +
</source>
 +
: Please note that when you run the "sudo" command the first time, it asks you for the user's password (i.e. user student's password). Let's now remote the "tree" package:<source lang='bash'>
 +
[student@centos7 ~]$ yum remove tree -y
 +
Loaded plugins: fastestmirror
 +
You need to be root to perform this command.
 +
[student@centos7 ~]$ sudo yum remove tree -y
 +
Loaded plugins: fastestmirror
 +
Resolving Dependencies
 +
--> Running transaction check
 +
---> Package tree.x86_64 0:1.6.0-10.el7 will be erased
 +
--> Finished Dependency Resolution
  
−
<pre>$ fab --fabfile=fabfile.py -H 192.168.56.11 getHostname
+
Dependencies Resolved
−
[192.168.56.11] Executing task 'getHostname'
 
−
[192.168.56.11] run: hostname
 
−
[192.168.56.11] out: www
 
−
[192.168.56.11] out:
 
  
−
worker1
+
========================================================================================================================
 +
Package                  Arch                      Version                            Repository                Size
 +
========================================================================================================================
 +
Removing:
 +
tree                    x86_64                    1.6.0-10.el7                      @base                      87 k
  
−
Done.
+
Transaction Summary
−
Disconnecting from 192.168.56.11... done.
+
========================================================================================================================
−
</pre>
+
Remove  1 Package
  
−
: In the above you have:
+
Installed size: 87 k
−
:* Lines with an IP address telling you which worker the output is for/from.
+
Downloading packages:
−
:* Messages from the controller (e.g. "Executing task...", and "run: ...").
+
Running transaction check
−
:* Output from the worker ("out: ...")
+
Running transaction test
−
:* Output on the controller from your fab file ("worker1" which came from the "print()" call)
+
Transaction test succeeded
 +
Running transaction
 +
  Erasing    : tree-1.6.0-10.el7.x86_64                                                                            1/1
 +
  Verifying  : tree-1.6.0-10.el7.x86_64                                                                            1/1
  
−
:You should get used to the above. It's a lot of output but it's important to understand where every part is coming from, so you are able to debug problems when they happen.
+
Removed:
 +
  tree.x86_64 0:1.6.0-10.el7
  
−
== Part 2: Set up web server ==
+
Complete!
 +
[student@centos7 ~]$
 +
</source>
 +
: The above tests confirm that the student user is allowed to run the yum command to install and remove rpm package. Now let's logout from the VM and go back to matrix. On matrix, try to run the sudo command using SSH:<source lang='bash'>
 +
[student@centos7 ~]$ exit
 +
logout
 +
Connection to myvmlab.senecacollege.ca closed.
 +
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7211 student@myvmlab.senecacollege.ca "sudo yum install tree -y"
 +
sudo: no tty present and no askpass program specified
 +
[raymond.chan@mtrx-node05pd lab8]$
 +
</source>
 +
: The above error indicated that you need a tty for the SSH session to prompt you for the sudo password. Please look up the ssh man page to find out the option which turn on a tty for the SSH session.
  
−
:Let's pretend that we needed to deploy a web server on several machines. We'll set up a simple example of such a deployment here.
+
=== Run the privileged yum command on remote machine using ad-hoc fab command ===
−
 
+
: Let's try the corresponding ad-hoc fab command on your VM:<source lang='bash'>
−
=== Install Apache ===
+
fab --host=myvmlab.senecacollege.ca --port=7200 --user=student -- 'sudo yum install tree -y'
−
 
+
</source>
−
:Add a setupWebServer() function to your python file:
+
: Type in your user student's password when prompted for "sudo password", the yum install command to install the tree rpm package should be executed successfully. If the tree rpm package is already installed, you can remove it with the following ad-hoc fab command: <source lang='bash'>
−
 
+
fab --host=myvmlab.senecacollege.ca --port=7200 --user=student -- 'sudo yum remove tree -y'
−
:<source lang="python"># Will set up a working web server with a pre-built website
 
−
def setupWebServer():
 
−
    run("hostnamectl set-hostname www")
 
−
    run("yum install httpd")
 
−
    run("systemctl enable httpd")
 
−
    run("systemctl start httpd")
 
 
</source>
 
</source>
 +
: Try remove the "tree" rpm package with the appropriate ad-hoc fab command.
  
−
:Note that each call to "run()" will run a command on the worker. In this function we set the hostname of the machine to "www", install Apache, enable the Apache service, and start that service now. Pretty simple commands.
+
= INVESTIGATION 3: Running the fab command in script mode =
 +
: From investigation 2, we can see that running '''fab''' in ad-hoc mode is quick, straight forward, and easy. However, the rich output generated can not be easily captured and processed. If you have a need to capture and process the output generated by the commands executed on the remote machines, the solution is to run the '''fab''' command in script mode.
 +
: The first step in running the '''fab''' command in script mode is to create a fabric script file.
 +
: Let's start with a simple fabric script file to demonstrate some basic concepts that use the API from the Fabric python library.
 +
: On matrix, cd to your lab8 directory and create a simple fabric script file named '''fabfile.py''' (this is the default filename used by the fab command when you invoke it without the '-f' optino):
  
−
:If you try to run it the same way as before:
+
== PART 1: Non-privileged task example ==
 +
===Create non-privileged tasks: Getting the hostname of remote machines===
 +
: Add the following contents to the default fabric script called "fabfile.py" in your lab8 directory:<source lang="python">
 +
from fabric.api import *
  
−
<pre>$ fab --fabfile=fabfile.py -H 192.168.56.11 setupWebServer</pre>
+
# set the name of the user login to the remote host
 +
env.user = 'student'
  
−
:You'll find that yum prompts you to answer questions, which you don't want to do in an automated environment. And also yum prints too much output, which also isn't helpful in an automated environment. We'll fix it by adding two switches to yum: "-y" and "-d1":
+
# Define the task to get the hostname of remote machines:
 +
def getHostname():
 +
    name = run("hostname")
 +
    print("The host name is:",name)
 +
</source>
  
−
:Notice also that all of the four commands can be run as many times as you want, the result will be the same. This is not always so easy.
+
: To check for syntax error in the fabric script, run the following command in the lab8 directory where it contains the fabric script named "fabfile.py":<source lang="bash">
 +
fab -l
 +
</source>
 +
: you should get a list of tasks defined in your fabfile.py:<source lang="bash">
 +
[rchan@centos7 lab8]$ fab -l
 +
Available commands:
  
−
:At this point if you log in to worker1 - you should see a new hostname, and httpd installed and running (try with "systemctl status").
+
    getHostname
 +
</source>
 +
: To perform the task of getHostname on your VM (replace with the actual port # for connecting to your VM), run the fab command on matrix:<source lang="bash">
 +
[raymond.chan@mtrx-node05pd lab8]$ fab --hosts=myvmlab.senecacollege.ca --port=7200 getHostname
 +
[myvmlab.senecacollege.ca] Executing task 'getHostname'
 +
[myvmlab.senecacollege.ca] run: hostname
 +
[myvmlab.senecacollege.ca] out: centos7
 +
[myvmlab.senecacollege.ca] out:
  
−
=== Deploy a website ===
+
The host name is: centos7
  
−
:Now that we have a web server running, we also want to put a website on it. The website can be of any complexity, but to keep this demonstration simple we'll have a single HTML file. You can pretend that it's as complex as you like. Create an '''index.html''' file like this:
+
Done.
−
 
+
Disconnecting from myvmlab.senecacollege.ca:7200... done.
−
:<source lang="html"><h1>My fancy web server</h1></source>
+
[raymond.chan@mtrx-node05pd lab8]$
−
 
 
−
:And since we're pretending that it's a large website with many files and directories, we'll compress it into an archive named '''webcontents.tar.bz2''' using a tar command. You've done this since OPS235.
 
−
 
 
−
:Once you have your archive, make sure it's in the same directory as your fab file. Then add the following to your setupWebServer() function:
 
−
 
 
−
:<source lang="python">
 
−
    with cd("/var/www/html/"):
 
−
        put("webcontents.tar.bz2", ".")
 
−
        run("tar xvf webcontents.tar.bz2")
 
−
        run("rm webcontents.tar.bz2")
 
 
</source>
 
</source>
 +
: Notice that there is no need to specify the user name at the '''fab''' command line since we defined it in the fabric script file (env.user = 'student'). Also notice that we can capture the host name returned from the "hostname" command and print it out together with an descriptive text in a line.
  
−
:There is something weird in the code above that you haven't seen before but it's required for some uses of Fabric: the '''with''' statement.
+
:In the above executed '''fab''' command, the fab program imports the fabric script named "fabfile.py" and execute the getHostname function on the VM connect at port 7200 on myvmlab.senecacollege.ca. Note that the port number for your first will likely be of a different value.
  
−
:The problem is that separate '''run''' commands each execute in a brand new session, each with its own shell. They are not like separate lines in a single shell script even though they look like they should be.
+
: If you did all the setup right and you got a password prompt when execute the above command, read the prompt carefully and see who's password it was prompting you for. If it is not for the user student, verify that you have the following line in your fabfile.py and you can ssh to your VM as the user student without password:
  
−
:That means if you run a cd command and then a tar command separately - the tar command will not run in the directory where you think it will. In order to fix this you have to nest commands inside a '''with''' - it's like a '''run''' but with persistant results.
+
:<source lang="python">env.user = 'student'</source>
  
−
:The code we added to the function will cd to the default web site directory on the worker, upload your web contents tarball from your controller to that directory on the worker, extract it, and delete the tarball.
+
: In the above output from the '''fab''' command, you have:
 +
:* Lines with the FQDN of the remote machine you are working on.
 +
:* Messages from the controller workstation (e.g. "Executing task...", and "run: ...").
 +
:* Output from the remote machine ("out: ...")
 +
:* Output generated on the controller workstation from your fab file (the print statement)
  
−
:After it's done - you should have a working web server and simple website on your worker1.
+
:You should get used to the above messages from the '''fab''' command. It's a lot of output but it's important to understand where every part is coming from, so you are able to debug problems when they happen.
  
−
:Except you won't be able to access it because of the firewall. We'll deal with that in the next section.
+
== PART 2: Privileged Tasks Examples ==
 +
===Creat privileged tasks: install and remove rpm package on remote machines===
 +
: Add the following two new functions to the end of the fabric script "fabfile.py" in your lab8 directory:<source lang='bash'>
  
−
== Part 2: Set up the firewall ==
+
def installPackage(pkg='dummy'):
 +
    cmd = 'yum install ' + pkg + ' -y'
 +
    status = sudo(cmd)
 +
    print(status)
  
−
: Recall that in our OPS courses we've been using iptables instead of firewalld, which is installed by default in CentOS. Let's make sure that our workers have that set up as well. In the same '''fabfile.py''' you've been using all along, add a new function like this:
+
def removePackage(pkg):
 +
    if pkg == '':
 +
      cmd = 'yum remove dummy -y'
 +
    else:
 +
      cmd = 'yum remove ' + pkg + ' -y'
 +
    status = sudo(cmd)
 +
    print(status)
 +
</source>
 +
: Note that both functions take one function argument in different ways. However, if no function argument is passed when calling the function, both will default to a string value of "dummy". Both functions call the sudo() from the fabric.api to execute the command contained in the "cmd" object on the remote machine via sudo.
 +
: To check for any syntax error in your updated fabric script, run the following command in the same directory as the fabfile.py:<source lang='bash'>
 +
fab -l
 +
</source>
 +
: You should get a list of tasks defined similar to the following:<source lang='bash'>
 +
[raymond.chan@mtrx-node05pd lab8]$ fab -l
 +
Available commands:
  
−
: <source lang="python">
+
     getHostname
−
# Will uninstall firewalld and replace it with iptables
+
     installPackage
−
def setupFirewall():
+
     removePackage
−
     run("yum -y -d1 remove firewalld")
+
[raymond.chan@mtrx-node05pd lab8]$
−
     run("yum -y -d1 install iptables-services")
 
−
     run("systemctl enable iptables")
 
−
    run("systemctl start iptables")
 
 
</source>
 
</source>
 +
: If you only need to connect to the same remote machine, you can specify the host and port number in the fabfile.py to save some typing when executing the fab command. Add the following two lines after the env.user line in your fabfile.py:<source lang='bash'>
 +
env.port = '7200' # <-- please replace with the actual value of your VM's port number
 +
env.hosts =['myvmlab.senecacollege.ca']
 +
</source>
 +
: You can also store the user's password in this file so that it will respond to the "sudo password" prompt for sudo() call. It is not safe to do so as you can configure the sudo module on the remote machine not to ask for sudo password.
 +
: Now you can run the fab command without the "--host" and "--port" option.
 +
: Run the following two fab commands, note the results and compare their difference:<source lang='bash'>
 +
fab installPackage
  
−
: That should by now look prett obvious. On the worker you're going to uninstall firewalld, install iptables, and make sure that the iptables service is running.
+
fab installPackage:tree
 +
</source>
 +
: Run the following two fab commands, note the results and compare their difference:<source lang='bash'>
 +
fab removePackage
  
−
: Execute the function for worker1 and double-check that it worked.
+
fab removePackage:tree
 +
</source>
  
−
=== Allow access to Apache through the firewall ===
+
== Part 2: Create remote task for updating rpm packages ==
 +
: Add a new function called "updatePackage" to your fabfile.py according to the following requirements:
 +
:* Accept optional function argument as the rpm package name
 +
:* If no function argument was given when called, default to all the packages installed
 +
: The output of the updatePackage when executed, should produce similar output as shown below:
 +
:1. Update a single package:<source lang='bash'>
 +
fab updatePackage:tree
 +
</source>
 +
: Sample output:<source lang='bash'>
 +
[raymond.chan@mtrx-node05pd lab8]$ fab updatePackage:tree
 +
[myvmlab.senecacollege.ca] Executing task 'updatePackage'
 +
[myvmlab.senecacollege.ca] sudo: yum update tree -y
 +
[myvmlab.senecacollege.ca] out: sudo password:
 +
[myvmlab.senecacollege.ca] out: Loaded plugins: fastestmirror
 +
[myvmlab.senecacollege.ca] out: Loading mirror speeds from cached hostfile
 +
[myvmlab.senecacollege.ca] out:  * base: less.cogeco.net
 +
[myvmlab.senecacollege.ca] out:  * extras: centos.mirror.ca.planethoster.net
 +
[myvmlab.senecacollege.ca] out:  * updates: less.cogeco.net
 +
[myvmlab.senecacollege.ca] out: No packages marked for update
 +
[myvmlab.senecacollege.ca] out:
  
−
: The default setup of iptables also doesn't allow access to our web server. We'll need to add some more to our function to allow it. This would probably make more sense in setupWebServer() but for now let's put it into setupFirewall():
+
Loaded plugins: fastestmirror
 +
Loading mirror speeds from cached hostfile
 +
* base: less.cogeco.net
 +
* extras: centos.mirror.ca.planethoster.net
 +
* updates: less.cogeco.net
 +
No packages marked for update
  
−
: <source lang="python">
+
Done.
−
    run("iptables -I INPUT -p tcp --dport 80 -j ACCEPT")
+
Disconnecting from myvmlab.senecacollege.ca:7200... done.
−
    run("iptables-save > /etc/sysconfig/iptables")
+
[raymond.chan@mtrx-node05pd lab8]$
 
</source>
 
</source>
−
 
+
:2. Update all installed package:<source lang='bash'>
−
: Easy enough, but there's on problem - if we run this more than once, we're going to end up with duplicate iptables rules for port 80 (check with iptables -L).
+
fab updatePackage:
−
 
 
−
: In order to avoid that - we have to first check whether the rule exists before we add it. We can do that like this:
 
−
 
 
−
: <source lang="bash">iptables -C INPUT -p tcp --dport 80 -j ACCEPT"</source>
 
−
 
 
−
: Unfortunately that command answers "yes" or "no" by succeeding or failing depending on whether that rule exists. In Fabric when a command fails - the entire fab file execution stops, assuming that it's an unrecoverable error. We need to prevent that with another with statement:
 
−
 
 
−
: <source lang="python">
 
−
    with settings(warn_only=True):
 
−
        firewallAlreadySetUp = run("iptables -C INPUT -p tcp --dport 80 -j ACCEPT")
 
−
        if firewallAlreadySetUp.return_code == 1:
 
−
            ... move your iptables rules setup here ...
 
 
</source>
 
</source>
 +
: The following output had been trimmed, only showing the first few lines:<source lang='bash'>
 +
[myvmlab.senecacollege.ca] Executing task 'updatePackage'
 +
[myvmlab.senecacollege.ca] sudo: yum update -y
 +
[myvmlab.senecacollege.ca] out: sudo password:
 +
[myvmlab.senecacollege.ca] out: Loaded plugins: fastestmirror
 +
[myvmlab.senecacollege.ca] out: Loading mirror speeds from cached hostfile
 +
[myvmlab.senecacollege.ca] out:  * base: less.cogeco.net
 +
[myvmlab.senecacollege.ca] out:  * extras: centos.mirror.ca.planethoster.net
 +
[myvmlab.senecacollege.ca] out:  * updates: less.cogeco.net
 +
...
  
−
: Test your new setupFirewall function on worker1, and make sure it opens access to Apache but does not create duplicate rules every time it's run.
+
  Verifying  : systemd-219-73.el7_8.5.x86_64                                                                      53/54
 +
  Verifying  : systemd-libs-219-73.el7_8.5.x86_64                                                                54/54
  
−
= INVESTIGATION 3: Multiplying your work =
+
Removed:
 +
  kernel.x86_64 0:3.10.0-862.el7
  
−
: After completing all the previous parts of the lab - you should have a working fabfile.py with two working functions: setupFirewall() and setupWebServer().
+
Installed:
 +
  kernel.x86_64 0:3.10.0-1127.13.1.el7
  
−
'''** Optional **'''You were asked to test them on worker1. Now let's run these two functions on all your workers at the same time. The command is almost the same, except for the list of IP addresses:
+
Updated:
 +
  bind-export-libs.x86_64 32:9.11.4-16.P2.el7_8.6          binutils.x86_64 0:2.27-43.base.el7_8.1
 +
  ca-certificates.noarch 0:2020.2.41-70.0.el7_8            device-mapper.x86_64 7:1.02.164-7.el7_8.2
 +
  device-mapper-event.x86_64 7:1.02.164-7.el7_8.2          device-mapper-event-libs.x86_64 7:1.02.164-7.el7_8.2
 +
  device-mapper-libs.x86_64 7:1.02.164-7.el7_8.2          kernel-tools.x86_64 0:3.10.0-1127.13.1.el7
 +
  kernel-tools-libs.x86_64 0:3.10.0-1127.13.1.el7          lvm2.x86_64 7:2.02.186-7.el7_8.2
 +
  lvm2-libs.x86_64 7:2.02.186-7.el7_8.2                    microcode_ctl.x86_64 2:2.1-61.10.el7_8
 +
  net-snmp.x86_64 1:5.7.2-48.el7_8.1                      net-snmp-agent-libs.x86_64 1:5.7.2-48.el7_8.1
 +
  net-snmp-libs.x86_64 1:5.7.2-48.el7_8.1                  net-snmp-utils.x86_64 1:5.7.2-48.el7_8.1
 +
  ntp.x86_64 0:4.2.6p5-29.el7.centos.2                    ntpdate.x86_64 0:4.2.6p5-29.el7.centos.2
 +
  python-perf.x86_64 0:3.10.0-1127.13.1.el7                rsyslog.x86_64 0:8.24.0-52.el7_8.2
 +
  selinux-policy.noarch 0:3.13.1-266.el7_8.1              selinux-policy-targeted.noarch 0:3.13.1-266.el7_8.1
 +
  systemd.x86_64 0:219-73.el7_8.8                          systemd-libs.x86_64 0:219-73.el7_8.8
 +
  systemd-sysv.x86_64 0:219-73.el7_8.8                    yum-plugin-fastestmirror.noarch 0:1.1.31-54.el7_8
  
−
<source lang="bash">fab --fabfile=fabfile.py -H 192.168.56.11,192.168.56.12,192.168.56.13,192.168.56.14,192.168.56.15 setupWebServer</source>
+
Complete!
  
−
: Again - your IP addresses will be different but the command will be the same.
+
Done.
−
 
+
Disconnecting from myvmlab.senecacollege.ca:7200... done.
−
: You can also reconfigure the firewall on all the workers at the same time, using a command like this on your controller:
+
[raymond.chan@mtrx-node05pd lab8]$
−
 
+
</source>
−
<source lang="bash">fab --fabfile=fabfile.py -H 192.168.56.11,192.168.56.12,192.168.56.13,192.168.56.14,192.168.56.15 setupFirewall</source>
 
−
 
 
−
And imagine that you might have 10, 50, 100 servers to do this on - could you do it without the automation?
 
  
−
= Final Task - Apply fabfile.py to your VM on myvmlab =
+
= Lab Exercise: Create a Fabric task called makeUser() =
−
: Since your account on your vm on myvmlab is a regular user with sudo privilege. You need to make the following changes to your fabfile.py before applying it to your vm on myvmlab:
+
: Study the Fabric API run(), sudo(), and put() and utilize them to create a new task called makeUser()
−
:* Change env.user from 'root' to your account on your vm in myvmlab.
+
: The makeUser() function should perform the following:
−
:* Change all the commands that need super user privilege from calling the run() function to instead calling the sudo() function.
+
:* create a new user called "ops435p" with home directory "/home/ops435p".
−
: Test your updated fabfile.py until you get the same result as when you apply it to your own worker VM.
+
:* add it to the sudo group called "wheel".  
 +
:* ask your professor for a ssh public key and add it to the file named "authorized_keys" in the ~ops435p/.ssh directory. Make sure that you set the proper permissions on both the directory ~ops435p/.ssh and the file "~ops435p/.ssh/authorized_keys.
 +
:Add the makeUser() to your final version of fabfile.py.
 +
:Run the new task makeUser() on your VM.
 +
:Verify and confirm that your new makeUser() task is working correctly.
  
 
= LAB 8 SIGN-OFF (SHOW INSTRUCTOR) =
 
= LAB 8 SIGN-OFF (SHOW INSTRUCTOR) =
−
:'''Have Ready to Show Your Instructor:'''
+
: Complete all the parts of the lab and upload the version of your fabfile.py to Blackboard by the due date.
−
* Complete all the parts of the lab and show the version of your fabfile.py which works on your vm on myvmlab.  
 
−
 
 
−
= LAB REVIEW =
 
  
−
[[Category:OPS435-Python]]
+
[[Category:OPS435-Python]][[Category:rchan]]

Latest revision as of 19:00, 4 July 2020

LAB OBJECTIVES

0. Review SSH setup and remote shell execution
1. Explore the Fabric Python library and its command line tool "fab".
2. Create Fabric scripts utilizing Fabric's API to define tasks for the fab command.
3. Use the fab command to execute fabric script to perform pre-defined tasks on remote Linux machines.

Overview

Fabric is a Python library and command-line tool for streamlining the use of SSH for application deployment or system administration tasks. It has two major components:
  1. a command-line interface program called "fab" that lets you execute arbitrary Python functions
  2. a set of Python APIs that you can use and call in your Python functions to make executing shell commands over SSH much easier.
We are going use the Fabric API and its fab command to define and execute Python functions (or tasks), to automate interactions with remote Linux machines in this lab.

REFERENCE

1. These links are helpful for learning more about Fabric's features:
Category Resource Link
Official Fabric tutorial
[1]
Better Fabric tutorial
[2]
Official Fabric website
[3]
Please note that the version of Fabric installed on matrix.senecacollege.ca for this lab is 1.14 and it supports only Python version 2. The Fabric script files we are going to create in this lab have to meet Python version 2.x requirements. (e.g. print is a keyword, not a built-in function in Python 2.x)
2. You should have some experience on the following topics in OPS235 and or OPS335. Please review them to prepare for the activities in this lab:
  • create and configure a regular user on a Linux system.
  • configure and manage sudo privilege for a regular user
  • Configure sudoers using the visudo command
  • using the yum command to install, remove, and update rpm packages
  • Retrieve current firewall setting using the iptables -L -n -v command

INVESTIGATION 1: The Fabric Environment

The Fabric environment consists of the following components:
  1. Controller workstation - the machine that has the Fabric package installed and runs the "fab" command
    1. the Fabric Python Library - the fabric package (already installed on matrix)
    2. the Fabric API - fabric.api
    3. the Fabric command - fab: run Fabric script, name of the script is default to fabfile.py in the current working directory unless specified otherwise with the '-f' option.
    4. Fabric script: contains fabric environment object value and Python functions (or tasks) to be executed by the fab command.
  2. Remote machine: the target machine on which one or more Fabric tasks will be executed.
    1. running the ssh server daemon
    2. use public key (or password based) authentication for ssh connection

PART 1 - Configure and test your controller workstation

In this lab you will use your login account on matrix.senecacollege.ca as your Fabric controller workstation.
The Fabric package version 1.14.0 has already been installed on matrix.senecacollege.ca. You should have access to the fab command on matrix. Login to matrix.senecacollege.ca and run the following command to confirm the version of the fabric package:
fab --version
Type the following command to get the command line options of the fab command:
fab --help
You should get something similar to the following:
Usage: fab [options] <command>[:arg1,arg2=val2,host=foo,hosts='h1;h2',...] ...

Options:
  -h, --help            show this help message and exit
  -d NAME, --display=NAME
                        print detailed info about command NAME
  -F FORMAT, --list-format=FORMAT
                        formats --list, choices: short, normal, nested
  -I, --initial-password-prompt
                        Force password prompt up-front
  --initial-sudo-password-prompt
                        Force sudo password prompt up-front
  -l, --list            print list of possible commands and exit
  --set=KEY=VALUE,...   comma separated KEY=VALUE pairs to set Fab env vars
  --shortlist           alias for -F short --list
  -V, --version         show program's version number and exit
  -a, --no_agent        don't use the running SSH agent
  -A, --forward-agent   forward local agent to remote end
  --abort-on-prompts    abort instead of prompting (for password, host, etc)
  -c PATH, --config=PATH
                        specify location of config file to use
  --colorize-errors     Color error output
  -D, --disable-known-hosts
                        do not load user known_hosts file
  -e, --eagerly-disconnect
                        disconnect from hosts as soon as possible
  -f PATH, --fabfile=PATH
                        python module file to import, e.g. '../other.py'
  -g HOST, --gateway=HOST
                        gateway host to connect through
  --gss-auth            Use GSS-API authentication
  --gss-deleg           Delegate GSS-API client credentials or not
  --gss-kex             Perform GSS-API Key Exchange and user authentication
  --hide=LEVELS         comma-separated list of output levels to hide
  -H HOSTS, --hosts=HOSTS
                        comma-separated list of hosts to operate on
  -i PATH               path to SSH private key file. May be repeated.
  -k, --no-keys         don't load private key files from ~/.ssh/
  --keepalive=N         enables a keepalive every N seconds
  --linewise            print line-by-line instead of byte-by-byte
  -n M, --connection-attempts=M
                        make M attempts to connect before giving up
  --no-pty              do not use pseudo-terminal in run/sudo
  -p PASSWORD, --password=PASSWORD
                        password for use with authentication and/or sudo
  -P, --parallel        default to parallel execution method
  --port=PORT           SSH connection port
  -r, --reject-unknown-hosts
                        reject unknown hosts
  --sudo-password=SUDO_PASSWORD
                        password for use with sudo only
  --system-known-hosts=SYSTEM_KNOWN_HOSTS
                        load system known_hosts file before reading user
                        known_hosts
  -R ROLES, --roles=ROLES
                        comma-separated list of roles to operate on
  -s SHELL, --shell=SHELL
                        specify a new shell, defaults to '/bin/bash -l -c'
  --show=LEVELS         comma-separated list of output levels to show
  --skip-bad-hosts      skip over hosts that can't be reached
  --skip-unknown-tasks  skip over unknown tasks
  --ssh-config-path=PATH
                        Path to SSH config file
  -t N, --timeout=N     set connection timeout to N seconds
  -T N, --command-timeout=N
                        set remote command timeout to N seconds
  -u USER, --user=USER  username to use when connecting to remote hosts
  -w, --warn-only       warn, instead of abort, when commands fail
  -x HOSTS, --exclude-hosts=HOSTS
                        comma-separated list of hosts to exclude
  -z INT, --pool-size=INT
                        number of concurrent processes to use in parallel mode

Please note and study the following command-line options as they will be used in some of the activities in this lab:

  1. -H,
  2. -f,
  3. -i,
  4. -l,
  5. --port
  6. --user
  7. --initial-sudo-password-prompt

PART 2: Connect to VM in myvmlab.senecacollege.ca

You should have received an email from ITS containing the following information:
  • account name: (usually 'student')
  • password: (let's assume it is 'P@ssw0rd' for the following instruction in this lab)
  • port number for SSH access via myvmlab.senecacollege.ca (e.g. 7200)
This VM will be used as the remote Linux machine in our Fabric environment. Login to matrix and try the following SSH command to test the connectivity between matrix and your assignment VM:
 [raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca
 student@myvmlab.senecacollege.ca's password:
 Last login: Fri Jul  3 11:06:24 2020 from mtrx-node05pd.dcm.senecacollege.ca
Once you are on your VM, try the following commands: hostname, id, and df, and record the results for later comparison with the results of other commands:
[student@centos7 ~]$ hostname
centos7
[student@centos7 ~]$ id
uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
[student@centos7 ~]$ df
Filesystem              1K-blocks    Used Available Use% Mounted on
devtmpfs                   878260       0    878260   0% /dev
tmpfs                      889792       0    889792   0% /dev/shm
tmpfs                      889792    9492    880300   2% /run
tmpfs                      889792       0    889792   0% /sys/fs/cgroup
/dev/mapper/centos-root  38680112 1745524  36934588   5% /
/dev/sda2                 1038336  331228    707108  32% /boot
/dev/sda1                  204580   11296    193284   6% /boot/efi
/dev/mapper/centos-home  18880512   33160  18847352   1% /home
tmpfs                      177960       0    177960   0% /run/user/1002
Logout from your VM and get back to matrix.
The previous SSH command when executed successfully, created a login shell on the remote machine. If the previous SSH command is followed by a specific bash command, it will be executed on the remote host instead of creating a login shell. Consider the following:
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca 'hostname;id;df'
student@myvmlab.senecacollege.ca's password:
centos7
uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
Filesystem              1K-blocks    Used Available Use% Mounted on
devtmpfs                   878260       0    878260   0% /dev
tmpfs                      889792       0    889792   0% /dev/shm
tmpfs                      889792    9492    880300   2% /run
tmpfs                      889792       0    889792   0% /sys/fs/cgroup
/dev/mapper/centos-root  38680112 1745608  36934504   5% /
/dev/sda2                 1038336  331228    707108  32% /boot
/dev/sda1                  204580   11296    193284   6% /boot/efi
/dev/mapper/centos-home  18880512   33160  18847352   1% /home
tmpfs                      177960       0    177960   0% /run/user/1002
The three shell commands: hostname, id, and df were executed sequentially. Compare the outputs above with the previous results when executing the corresponding commands in the login shell.
Please note that you were asked to provide the user's password for every SSH connection.

PART 3: Set up SSH login with public key authentication

In order for your controller workstation to automate tasks execution on your VM, you need to configure your VM to SSH public key authentication instead of password authentication. You've done this in both OPS235 and OPS335, and here is a summary on how to do it between your account on matrix and your VM:
Create a new SSH key pair (one private, and one public) under your account on matrix.senecacollege.ca.
Once you have both keys, you can use the ssh-copy-id command to copy your public key to the student account on your VM, replace the port number with the correct value for your VM:
ssh-copy-id -i ~/.ssh/id_rsa.pub -p 7200 student@myvmlab.senecacollege.ca
The above command should add the contents of your pub key to ~/.ssh/authorized_keys under your student account on your VM.
Verify and confirm that your account on matrix can SSH to your VM as 'student' without prompting for a password:
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca
Last login: Fri Jul  3 12:46:19 2020 from mtrx-node05pd.dcm.senecacollege.ca
[student@centos7 ~]$ exit
logout
Connection to myvmlab.senecacollege.ca closed.

[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca 'date;hostname;id'
Fri Jul  3 12:55:22 EDT 2020
centos7
uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
[raymond.chan@mtrx-node05pd lab8]$
If you got similar result as above, you have successfully configure your controller workstation and your VM to use public key authentication.

INVESTIGATION 2 - Running the fab command in ad-hoc mode

The fab command relies on SSH to make the connection to the remote machine before executing the intended commands. The fab command can run in ad-hoc mode:
fab [options] -- [shell commands]
When running the fab command in ad-hoc mode, it is very similar to running the SSH with commands attached at the end.

PART 1: running non-privileged shell commands on remote machines

In the following example, we use the fab to execute the "date", "hostname", and "id" command remotely on our VM. Try the following ad-hoc fab commands and record their results for later use, replace the port number with the correct value for your VM:
[raymond.chan@mtrx-node05pd lab8]$ fab --host=myvmlab.senecacollege.ca --port=7200 --user=student -- 'date;hostname;id'
[myvmlab.senecacollege.ca] Executing task '<remainder>'
[myvmlab.senecacollege.ca] run: date;hostname;id
[myvmlab.senecacollege.ca] out: Fri Jul  3 13:05:39 EDT 2020
[myvmlab.senecacollege.ca] out: centos7
[myvmlab.senecacollege.ca] out: uid=1002(student) gid=1002(student) groups=1002(student),10(wheel)
[myvmlab.senecacollege.ca] out:


Done.
Disconnecting from myvmlab.senecacollege.ca:7200... done.
[raymond.chan@mtrx-node05pd lab8]$
Note that there is no password prompting if you complete part 3 successfully, otherwise, the SSH server daemon on your VM will prompt you for a password. The output from the fab's ad-hoc mode is not much different from the SSH command with shell command attached at the end, however, please note that the additional information on the output from the fab command can be very useful for record keeping purpose - what has been done and whether the commands had been carried out successfully or not.

PART 2: running privileged commands on remote machines

We say that running an ad-hoc fab command is very similar to the SSH command with shell commands attached at the end. Let's try both with privileged commands, like the "yum" command.

Run the "yum" command on remote machine with SSH

By default, your VM doesn't have the "tree" rpm package installed. You can verify this with the following SSH command (remember to replace the port number with the correct value for your VM):
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca "yum list tree"
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: centos.mirror.colo-serv.net
 * extras: centos.mirror.colo-serv.net
 * updates: centos.mirror.ca.planethoster.net
Available Packages
tree.x86_64                          1.6.0-10.el7                           base
[raymond.chan@mtrx-node05pd lab8]$
Please note that the tree package is "Available", but not yet installed.
Let't try to install the "tree" package with the shell command "yum install tree -y":
[raymond.chan@mtrx-node05pd lab8]$ ssh -p student@myvmlab.senecacollege.ca "yum install tree -y"
Loaded plugins: fastestmirror
You need to be root to perform this command.
Using the "yum" command to query rpm package doesn't need special privilege, however, it does when you try to install or remove rpm packages.
Your "student" account on your VM was configured to allow you to run the "sudo" command to perform software management using the "yum" command. Let's login to your VM and try the following "sudo" command to install and then remove the "tree" rpm package:
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7200 student@myvmlab.senecacollege.ca
Last login: Fri Jul  3 16:51:07 2020 from mtrx-node05pd.dcm.senecacollege.ca
[student@centos7 ~]$ sudo yum install tree -y
[sudo] password for student:
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: less.cogeco.net
 * extras: centos.mirror.colo-serv.net
 * updates: mirror.calgah.com
Resolving Dependencies
--> Running transaction check
---> Package tree.x86_64 0:1.6.0-10.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

========================================================================================================================
 Package                  Arch                       Version                             Repository                Size
========================================================================================================================
Installing:
 tree                     x86_64                     1.6.0-10.el7                        base                      46 k

Transaction Summary
========================================================================================================================
Install  1 Package

Total download size: 46 k
Installed size: 87 k
Downloading packages:
tree-1.6.0-10.el7.x86_64.rpm                                                                     |  46 kB  00:00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : tree-1.6.0-10.el7.x86_64                                                                             1/1
  Verifying  : tree-1.6.0-10.el7.x86_64                                                                             1/1

Installed:
  tree.x86_64 0:1.6.0-10.el7

Complete!
[student@centos7 ~]$
Please note that when you run the "sudo" command the first time, it asks you for the user's password (i.e. user student's password). Let's now remote the "tree" package:
[student@centos7 ~]$ yum remove tree -y
Loaded plugins: fastestmirror
You need to be root to perform this command.
[student@centos7 ~]$ sudo yum remove tree -y
Loaded plugins: fastestmirror
Resolving Dependencies
--> Running transaction check
---> Package tree.x86_64 0:1.6.0-10.el7 will be erased
--> Finished Dependency Resolution

Dependencies Resolved

========================================================================================================================
 Package                  Arch                       Version                            Repository                 Size
========================================================================================================================
Removing:
 tree                     x86_64                     1.6.0-10.el7                       @base                      87 k

Transaction Summary
========================================================================================================================
Remove  1 Package

Installed size: 87 k
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Erasing    : tree-1.6.0-10.el7.x86_64                                                                             1/1
  Verifying  : tree-1.6.0-10.el7.x86_64                                                                             1/1

Removed:
  tree.x86_64 0:1.6.0-10.el7

Complete!
[student@centos7 ~]$
The above tests confirm that the student user is allowed to run the yum command to install and remove rpm package. Now let's logout from the VM and go back to matrix. On matrix, try to run the sudo command using SSH:
[student@centos7 ~]$ exit
logout
Connection to myvmlab.senecacollege.ca closed.
[raymond.chan@mtrx-node05pd lab8]$ ssh -p 7211 student@myvmlab.senecacollege.ca "sudo yum install tree -y"
sudo: no tty present and no askpass program specified
[raymond.chan@mtrx-node05pd lab8]$
The above error indicated that you need a tty for the SSH session to prompt you for the sudo password. Please look up the ssh man page to find out the option which turn on a tty for the SSH session.

Run the privileged yum command on remote machine using ad-hoc fab command

Let's try the corresponding ad-hoc fab command on your VM:
fab --host=myvmlab.senecacollege.ca --port=7200 --user=student -- 'sudo yum install tree -y'
Type in your user student's password when prompted for "sudo password", the yum install command to install the tree rpm package should be executed successfully. If the tree rpm package is already installed, you can remove it with the following ad-hoc fab command: 
fab --host=myvmlab.senecacollege.ca --port=7200 --user=student -- 'sudo yum remove tree -y'
Try remove the "tree" rpm package with the appropriate ad-hoc fab command.

INVESTIGATION 3: Running the fab command in script mode

From investigation 2, we can see that running fab in ad-hoc mode is quick, straight forward, and easy. However, the rich output generated can not be easily captured and processed. If you have a need to capture and process the output generated by the commands executed on the remote machines, the solution is to run the fab command in script mode.
The first step in running the fab command in script mode is to create a fabric script file.
Let's start with a simple fabric script file to demonstrate some basic concepts that use the API from the Fabric python library.
On matrix, cd to your lab8 directory and create a simple fabric script file named fabfile.py (this is the default filename used by the fab command when you invoke it without the '-f' optino):

PART 1: Non-privileged task example

Create non-privileged tasks: Getting the hostname of remote machines

Add the following contents to the default fabric script called "fabfile.py" in your lab8 directory:
from fabric.api import *

# set the name of the user login to the remote host
env.user = 'student'

# Define the task to get the hostname of remote machines:
def getHostname():
    name = run("hostname")
    print("The host name is:",name)
To check for syntax error in the fabric script, run the following command in the lab8 directory where it contains the fabric script named "fabfile.py":
fab -l
you should get a list of tasks defined in your fabfile.py:
[rchan@centos7 lab8]$ fab -l
Available commands:

    getHostname
To perform the task of getHostname on your VM (replace with the actual port # for connecting to your VM), run the fab command on matrix:
[raymond.chan@mtrx-node05pd lab8]$ fab --hosts=myvmlab.senecacollege.ca --port=7200 getHostname
[myvmlab.senecacollege.ca] Executing task 'getHostname'
[myvmlab.senecacollege.ca] run: hostname
[myvmlab.senecacollege.ca] out: centos7
[myvmlab.senecacollege.ca] out:

The host name is: centos7

Done.
Disconnecting from myvmlab.senecacollege.ca:7200... done.
[raymond.chan@mtrx-node05pd lab8]$
Notice that there is no need to specify the user name at the fab command line since we defined it in the fabric script file (env.user = 'student'). Also notice that we can capture the host name returned from the "hostname" command and print it out together with an descriptive text in a line.
In the above executed fab command, the fab program imports the fabric script named "fabfile.py" and execute the getHostname function on the VM connect at port 7200 on myvmlab.senecacollege.ca. Note that the port number for your first will likely be of a different value.
If you did all the setup right and you got a password prompt when execute the above command, read the prompt carefully and see who's password it was prompting you for. If it is not for the user student, verify that you have the following line in your fabfile.py and you can ssh to your VM as the user student without password:
env.user = 'student'
In the above output from the fab command, you have:
  • Lines with the FQDN of the remote machine you are working on.
  • Messages from the controller workstation (e.g. "Executing task...", and "run: ...").
  • Output from the remote machine ("out: ...")
  • Output generated on the controller workstation from your fab file (the print statement)
You should get used to the above messages from the fab command. It's a lot of output but it's important to understand where every part is coming from, so you are able to debug problems when they happen.

PART 2: Privileged Tasks Examples

Creat privileged tasks: install and remove rpm package on remote machines

Add the following two new functions to the end of the fabric script "fabfile.py" in your lab8 directory:
def installPackage(pkg='dummy'):
    cmd = 'yum install ' + pkg + ' -y'
    status = sudo(cmd)
    print(status)

def removePackage(pkg):
    if pkg == '':
       cmd = 'yum remove dummy -y'
    else:
       cmd = 'yum remove ' + pkg + ' -y'
    status = sudo(cmd)
    print(status)
Note that both functions take one function argument in different ways. However, if no function argument is passed when calling the function, both will default to a string value of "dummy". Both functions call the sudo() from the fabric.api to execute the command contained in the "cmd" object on the remote machine via sudo.
To check for any syntax error in your updated fabric script, run the following command in the same directory as the fabfile.py:
fab -l
You should get a list of tasks defined similar to the following:
[raymond.chan@mtrx-node05pd lab8]$ fab -l
Available commands:

    getHostname
    installPackage
    removePackage
[raymond.chan@mtrx-node05pd lab8]$
If you only need to connect to the same remote machine, you can specify the host and port number in the fabfile.py to save some typing when executing the fab command. Add the following two lines after the env.user line in your fabfile.py:
env.port = '7200' # <-- please replace with the actual value of your VM's port number
env.hosts =['myvmlab.senecacollege.ca']
You can also store the user's password in this file so that it will respond to the "sudo password" prompt for sudo() call. It is not safe to do so as you can configure the sudo module on the remote machine not to ask for sudo password.
Now you can run the fab command without the "--host" and "--port" option.
Run the following two fab commands, note the results and compare their difference:
fab installPackage

fab installPackage:tree
Run the following two fab commands, note the results and compare their difference:
fab removePackage

fab removePackage:tree

Part 2: Create remote task for updating rpm packages

Add a new function called "updatePackage" to your fabfile.py according to the following requirements:
  • Accept optional function argument as the rpm package name
  • If no function argument was given when called, default to all the packages installed
The output of the updatePackage when executed, should produce similar output as shown below:
1. Update a single package:
fab updatePackage:tree
Sample output:
[raymond.chan@mtrx-node05pd lab8]$ fab updatePackage:tree
[myvmlab.senecacollege.ca] Executing task 'updatePackage'
[myvmlab.senecacollege.ca] sudo: yum update tree -y
[myvmlab.senecacollege.ca] out: sudo password:
[myvmlab.senecacollege.ca] out: Loaded plugins: fastestmirror
[myvmlab.senecacollege.ca] out: Loading mirror speeds from cached hostfile
[myvmlab.senecacollege.ca] out:  * base: less.cogeco.net
[myvmlab.senecacollege.ca] out:  * extras: centos.mirror.ca.planethoster.net
[myvmlab.senecacollege.ca] out:  * updates: less.cogeco.net
[myvmlab.senecacollege.ca] out: No packages marked for update
[myvmlab.senecacollege.ca] out:

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: less.cogeco.net
 * extras: centos.mirror.ca.planethoster.net
 * updates: less.cogeco.net
No packages marked for update

Done.
Disconnecting from myvmlab.senecacollege.ca:7200... done.
[raymond.chan@mtrx-node05pd lab8]$
2. Update all installed package:
fab updatePackage:
The following output had been trimmed, only showing the first few lines:
[myvmlab.senecacollege.ca] Executing task 'updatePackage'
[myvmlab.senecacollege.ca] sudo: yum update -y
[myvmlab.senecacollege.ca] out: sudo password:
[myvmlab.senecacollege.ca] out: Loaded plugins: fastestmirror
[myvmlab.senecacollege.ca] out: Loading mirror speeds from cached hostfile
[myvmlab.senecacollege.ca] out:  * base: less.cogeco.net
[myvmlab.senecacollege.ca] out:  * extras: centos.mirror.ca.planethoster.net
[myvmlab.senecacollege.ca] out:  * updates: less.cogeco.net
...

  Verifying  : systemd-219-73.el7_8.5.x86_64                                                                      53/54
  Verifying  : systemd-libs-219-73.el7_8.5.x86_64                                                                 54/54

Removed:
  kernel.x86_64 0:3.10.0-862.el7

Installed:
  kernel.x86_64 0:3.10.0-1127.13.1.el7

Updated:
  bind-export-libs.x86_64 32:9.11.4-16.P2.el7_8.6          binutils.x86_64 0:2.27-43.base.el7_8.1
  ca-certificates.noarch 0:2020.2.41-70.0.el7_8            device-mapper.x86_64 7:1.02.164-7.el7_8.2
  device-mapper-event.x86_64 7:1.02.164-7.el7_8.2          device-mapper-event-libs.x86_64 7:1.02.164-7.el7_8.2
  device-mapper-libs.x86_64 7:1.02.164-7.el7_8.2           kernel-tools.x86_64 0:3.10.0-1127.13.1.el7
  kernel-tools-libs.x86_64 0:3.10.0-1127.13.1.el7          lvm2.x86_64 7:2.02.186-7.el7_8.2
  lvm2-libs.x86_64 7:2.02.186-7.el7_8.2                    microcode_ctl.x86_64 2:2.1-61.10.el7_8
  net-snmp.x86_64 1:5.7.2-48.el7_8.1                       net-snmp-agent-libs.x86_64 1:5.7.2-48.el7_8.1
  net-snmp-libs.x86_64 1:5.7.2-48.el7_8.1                  net-snmp-utils.x86_64 1:5.7.2-48.el7_8.1
  ntp.x86_64 0:4.2.6p5-29.el7.centos.2                     ntpdate.x86_64 0:4.2.6p5-29.el7.centos.2
  python-perf.x86_64 0:3.10.0-1127.13.1.el7                rsyslog.x86_64 0:8.24.0-52.el7_8.2
  selinux-policy.noarch 0:3.13.1-266.el7_8.1               selinux-policy-targeted.noarch 0:3.13.1-266.el7_8.1
  systemd.x86_64 0:219-73.el7_8.8                          systemd-libs.x86_64 0:219-73.el7_8.8
  systemd-sysv.x86_64 0:219-73.el7_8.8                     yum-plugin-fastestmirror.noarch 0:1.1.31-54.el7_8

Complete!

Done.
Disconnecting from myvmlab.senecacollege.ca:7200... done.
[raymond.chan@mtrx-node05pd lab8]$

Lab Exercise: Create a Fabric task called makeUser()

Study the Fabric API run(), sudo(), and put() and utilize them to create a new task called makeUser()
The makeUser() function should perform the following:
  • create a new user called "ops435p" with home directory "/home/ops435p".
  • add it to the sudo group called "wheel".
  • ask your professor for a ssh public key and add it to the file named "authorized_keys" in the ~ops435p/.ssh directory. Make sure that you set the proper permissions on both the directory ~ops435p/.ssh and the file "~ops435p/.ssh/authorized_keys.
Add the makeUser() to your final version of fabfile.py.
Run the new task makeUser() on your VM.
Verify and confirm that your new makeUser() task is working correctly.

LAB 8 SIGN-OFF (SHOW INSTRUCTOR)

Complete all the parts of the lab and upload the version of your fabfile.py to Blackboard by the due date.
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