OPS435 Ansible

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Revision as of 14:07, 24 November 2019 by Rchan (talk | contribs) (Part 1: Installing Ansible on CentOS 7)
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  1. Install and configure Ansible on a controller Linux machine
  2. Explore Ansible's ad hoc commands
  3. Explore Ansible's built-in modules
  4. Explore and create Ansible playbooks


Ansible is an agentless IT automation engine for automating cloud provisioning, configuration management, application deployment, intra-service orchestration, and many other IT system administration tasks.
Ansible uses no additional custom security infrastructure, and it uses a very simple human readable language called 'YAML', to compose an Ansible Playbook which allow you to describes the tasks you want to automate.


Investigation I: Introduction to Ansible

In this introduction, we explore the main components of the Ansible configuration management system and its operating environment. we also study a simple playbook for managing the configuration of a CentOS 7.x VM.
You need at least two VMs for this lab: one VM to be used as the control machine and one or more VMs to be used as the managed machines. You only need to install Ansible on the control machine.

Key Concepts when using Ansible

  • YAML - a human-readable data serialization language use by Ansible's playbooks. To know more, your can check out the wikipedia page here
  • Control machine - the host on which you use Ansible to execute tasks on the managed machines
  • Managed machine - a host that is configured by the control machine
  • Hosts file - contains information about machines to be managed - click here for sample hosts file
  • Ad hoc commands - a simple one-off task:
    • shell commands
      • ansible -a 'date'
      • ansible -a 'df'
      • ansible -a 'iptables -L -n -v' -u root
  • Built-in modules - code that performs a particular task such as copy a file, installing a package, etc:
    • copy module
      • ansible -m copy -a "src=/ops435/ansible.txt dest=/tmp/ansible.txt"
    • Package management
      • ansible -m yum -a "name=epel-release state=latest"
  • Playbooks - contains one or multiple plays, each play defines a set of repeatable tasks on one or more managed machines. Playbooks are written in YAML. Every play in the playbook is created with environment-specific parameters for the target machines:
    • ansible-playbook -i, setup_webserver.yaml
    • ansible-playbook firstrun.yaml

== Hardware and software required

Part 1: Installing Ansible on CentOS 7

You only need to install the "ansible" package on your control VM.
  • Login as a regular user, change to the directory ~/ops435/lab9
  • Issue the following command to install the "ansible" package:
    sudo yum install ansible -y
You may have to install the following dependent packages:
Dependencies Resolved

 Package                             Arch                  Version                       Repository             Size
 ansible                             noarch                2.9.1-1.el7                   epel                   17 M
Installing for dependencies:
 python-babel                        noarch                0.9.6-8.el7                   base                  1.4 M
 python-cffi                         x86_64                1.6.0-5.el7                   base                  218 k
 python-enum34                       noarch                1.0.4-1.el7                   base                   52 k
 python-httplib2                     noarch                0.9.2-1.el7                   extras                115 k
 python-idna                         noarch                2.4-1.el7                     base                   94 k
 python-jinja2                       noarch                2.7.2-4.el7                   base                  519 k
 python-markupsafe                   x86_64                0.11-10.el7                   base                   25 k
 python-paramiko                     noarch                2.1.1-9.el7                   base                  269 k
 python-ply                          noarch                3.4-11.el7                    base                  123 k
 python-pycparser                    noarch                2.14-1.el7                    base                  104 k
 python2-cryptography                x86_64                1.7.2-2.el7                   base                  502 k
 python2-jmespath                    noarch                0.9.0-3.el7                   extras                 39 k
 python2-pyasn1                      noarch                0.1.9-7.el7                   base                  100 k
 sshpass                             x86_64                1.06-2.el7                    extras                 21 k

Transaction Summary
Install  1 Package (+14 Dependent packages)

Total download size: 21 M
Installed size: 120 M
Is this ok [y/d/N]:
To confirm that you have Ansible installed, try the following command:
[rchan@c7-rchan ~]$ ansible --help
usage: ansible [-h] [--version] [-v] [-b] [--become-method BECOME_METHOD]
               [--become-user BECOME_USER] [-K] [-i INVENTORY] [--list-hosts]
               [-l SUBSET] [-P POLL_INTERVAL] [-B SECONDS] [-o] [-t TREE] [-k]
               [--private-key PRIVATE_KEY_FILE] [-u REMOTE_USER]
               [-c CONNECTION] [-T TIMEOUT]
               [--ssh-common-args SSH_COMMON_ARGS]
               [--sftp-extra-args SFTP_EXTRA_ARGS]
               [--scp-extra-args SCP_EXTRA_ARGS]
               [--ssh-extra-args SSH_EXTRA_ARGS] [-C] [--syntax-check] [-D]
               [-e EXTRA_VARS] [--vault-id VAULT_IDS]
               [--ask-vault-pass | --vault-password-file VAULT_PASSWORD_FILES]
               [-f FORKS] [-M MODULE_PATH] [--playbook-dir BASEDIR]
               [-a MODULE_ARGS] [-m MODULE_NAME]
Take a look of all the available command line options for the "ansible" command. There are a lots of options when running Ansible. Let's move on to try a few simple ones.

Part 2: Sample runs for some of the Ad hoc commands

[rchan@centos7 ansible]$ ansible -m copy -a "src=/home/rchan/ops435/ansible/ansible.txt dest=/tmp/ansible.txt" | SUCCESS => {
    "changed": true, 
    "checksum": "837affc90674fb92cdb0ebac6e49ad31a586b37e", 
    "dest": "/tmp/ansible.txt", 
    "gid": 1001, 
    "group": "rchan", 
    "md5sum": "78ae49d77d28d06173cf2194a3909732", 
    "mode": "0664", 
    "owner": "rchan", 
    "secontext": "unconfined_u:object_r:user_home_t:s0", 
    "size": 106, 
    "src": "/home/rchan/.ansible/tmp/ansible-tmp-1542902119.15-117618539513309/source", 
    "state": "file", 
    "uid": 1001
} is the remote machine's IP address.
"-m copy" tells ansible to use the copy module
after '-a' is the arguments to the copy module, which specify the source file and the destination for the copy action.
If you got the same "SUCCESS" message, login to the remote machine (in this example, it is and check the directory "/tmp" for the file ansible.txt.

Part 3: Sample runs for using some Ansible's built-in modules

"yum" is a built-in ansible module. You can get detail information about an ansible module with the following command:
    ansible-doc yum
The following command demonstrates how to install the "epel-release" package with the "yum" module:
[rchan@centos7 ansible]$ ansible -m yum -a "name=epel-release state=present" | SUCCESS => {
    "changed": false, 
    "msg": "", 
    "rc": 0, 
    "results": [
        "epel-release-7-11.noarch providing epel-release is already installed"

[rchan@centos7 ansible]$ ansible -m yum -a "name=epel-release state=present" -u root | SUCCESS => {
    "changed": false, 
    "msg": "", 
    "rc": 0, 
    "results": [
        "epel-release-7-11.noarch providing epel-release is already installed"

[rchan@centos7 ansible]$ ansible -m yum -a "name=epel-release state=latest" -u root | SUCCESS => {
    "changed": false, 
    "msg": "", 
    "rc": 0, 
    "results": [
        "All packages providing epel-release are up to date", 

Part 4: Gather software and hardware information available on remote machine

One of the main ansible module is called "setup", it is automatically called by ansible playbook to gather useful "facts" about remote hosts that can be used in ansible playbooks. It can also be executed directly by the ansible command (/usr/bin/ansible) to check what "facts" are available to a host.
[rchan@centos7 ansible]$ ansible -m setup | SUCCESS => {
    "ansible_facts": {
        "ansible_all_ipv4_addresses": [
        "ansible_all_ipv6_addresses": [
        "ansible_architecture": "x86_64", 
        "ansible_bios_date": "04/01/2014", 
        "ansible_bios_version": "1.9.1-5.el7_3.2", 
        "ansible_cmdline": {
            "BOOT_IMAGE": "/vmlinuz-3.10.0-862.14.4.el7.x86_64", 
            "LANG": "en_CA.UTF-8", 
            "console": "ttyS0", 
        "ansible_userspace_bits": "64", 
        "ansible_virtualization_role": "guest", 
        "ansible_virtualization_type": "kvm", 
        "module_setup": true
    "changed": false

Click here for complete contents of the above

Investigation II: Ansible Playbook

What is a playbook?

* Playbook is one of the core features of Ansible.
* Playbook tells Ansible what to execute by which user on the remote machine.
* Playbook is like a to-do list for Ansible
* Playbook is write in a simple human readable language called "YAML".
* Playbook links a task to an ansible module and provide needed arguments to the module which requires them.

Part 1: A playbook to update the /etc/motd file

Name: motd-play.yml

- hosts:
  user: root
    apache_version: 2.6
    motd_warning: 'WARNING: use by ICT faculty/students only.'
    testserver: yes
    - name: setup a MOTD
        dest: /etc/motd
        content: "{{ motd_warning }}"

Sample Run:

[rchan@centos7 playbooks]$ ansible-playbook motd-play.yml

PLAY [] **********************************************************

TASK [Gathering Facts] *********************************************************
ok: []

TASK [setup a MOTD] ************************************************************
changed: []

PLAY RECAP *********************************************************************             : ok=2    changed=1    unreachable=0    failed=0   

Part 2: A playbook to install and start Apache Server

Name: httpd-play.yml

- hosts:
  user: root
    apache_version: 2.6
    motd_warning: 'WARNING: use by ICT faculty/students only.'
    testserver: yes
    - name: install apache
      action: yum name=httpd state=installed
    - name: restart apache
        name: httpd
        state: restarted

Sample Run:

[rchan@centos7 playbooks]$ ansible-playbook httpd-play.yml

PLAY [] **********************************************************

TASK [Gathering Facts] *********************************************************
ok: []

TASK [install apache] **********************************************************
changed: []

TASK [restart apache] **********************************************************
changed: []

PLAY RECAP *********************************************************************             : ok=3    changed=2    unreachable=0    failed=0   


System requirements

  • You must have at lease two networked machines
    • control node - run ansible to configure remote node - need Ansible 2.x (latest version 2.7)
    • remote nodes - to be managed by the control node
  • You should be to ssh from your control node as a regular user to any of your remote nodes as root user without supplying a login password.
  • Python 2.7+ on all nodes


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