Ansible Practise

Introduction to Ansible and Basics.

Ansible Documentation

• https://docs.ansible.com/ansible/latest/index.html

Installing Ansible in centos

Ansible is part of the Extra Packages for Enterprise Linux (EPEL) repository so you need to install epel-release package first

$ sudo yum install epel-release

$ sudo yum repolist

Now you can go ahead and install ansible

$ sudo yum install ansible

Ansible Inventory

• Ansible can interact with one more servers at a time. To interact ansible will use

  • SSH for Linux
  • Power Shell Remoting for Windows

• Ansible is Agentless - No client software is needed on servers.

• Information about the target machines will be stored in a inventory file.

  • Default Inventory file for ansible is available at /etc/ansible/hosts

• Ansible Inventory Parameters

  • ansible_host - used to specify fqdn or ip address of a server
  • ansible_connection - Defines how ansible connects to target server (ssh, winrm etc)
  • ansible_port - Defines which port to connect to. (By default configured to port-22)
  • ansible_user - The login details ( linux - root/ windows - administrator)
  • ansible_ssh_pass - The ssh password for linux
  • ansible_password - The password for windows

A ansible Groups will be created like

[group1]
host1
host2
..

A ansible Parent child groups will be created like

[group1:children]
child_group1
child_group2
..

Sample Inventory Files by using Inventory Parameters are here.

• https://github.com/sumanth979/AnsiblePractise/blob/master/sample_inventory_file_1.yaml
• https://github.com/sumanth979/AnsiblePractise/blob/master/sample_inventory_file_2.yaml

To run an ansible command aganist a host

ansible <hostname> -m <modulename>
             &&
ansible <hostname> -a <command>             

To specify the inventory file:
ansible <hostname> -m <modulename> -i <inventoryfile>           

Ansible Playbooks

• Running a series of instructions on different servers in a sequence and restarting the servers in a particular order.
• How a Play Book is writtened:

Playbook - single YAML file
  * play - Defines a Set of activities(tasks) to be run n hosts.
    * Task - An action to be perfomed on the host
      * Execute a Command
      * Run a script
      * Install a package
      * Shutdown/Restart
      ...

• The each task execute by a Playbook is called Ansible Module

To get the list of modules available with ansible, use the following command:
ansible-doc -l

Ansible playbook help command

ansible-playbook --help

To run the ansible playbook

ansible-playbook <playbook name> -i <inventoryfile>

Ansible Modules

• Ansible Modules are categorized into different types. They are as follows:
  • system -> actions to be performed at system level. (modifying users, firewalls, stopping and starting services etc)
  • commands -> Used to execute commands or scripts on target machines.
  • Files -> Help to work with files
  • Databases
  • Cloud
  • windows -> to work with windows
  • ...

Ansible Variables

• Ansible Variables can create either in inventory file or in playbook file.
• Either we can create seperate file to maintain variable information.

To create a variable in playbook file

vars:
  dns_server: <server_value>

To use the variables in inventory file

# sample inventory file
server1 variable1=<value> variable2=<value>

To use the variables from an external file

# sample variable file - variable.yaml

variable1: <value>
variable2: <value>
variable3: <value>

Variable usage

It to use directly - `{{variableName}}`
Inside a sentence - Inside a {{variableName}} sentence.

Conditional Statements & Loops in Ansible

When Condition

• We can use AND and OR to check multiple conditions.

tasks:
  - name : <name>
    yum:
      name: nginx 
      state: present
    when: ansible_os_family == "RedHat"

Register Usage

• Register is used to store the value of the command executed.

Sample Usage:
    tasks:
        -
            shell: 'cat /etc/resolv.conf'
            register: command_output

Loops Usage

• loop previously names as [with_*] in ansible.
• To run same set of commands multiple times.

Sample Usage:
-
  name: create users
  hosts: localhost
  tasks:
   - user: name= '{{item}}' state=present
     loop:
       - user1
       - user2
       - user3
       ...

Sample Usage:
-
  name: create users
  hosts: localhost
  tasks:
   - user: name= '{{item.name}}' uid='{{item.id}}' state=present
     loop:
       - name: user1
         id: 1
       - name: user2
         id: 2
       - name: user3
         id: 3
       ...

Ansible Roles

• Asigning a role means

  • Installing pre-requisities
  • Installing packages
  • Configuring services
  • Configuring users and others

• Sample Roles are - mysql, nginx, redis, monitor, backup etc..

• For every task you no need to create your own role. You can make use of exsting roles (in ansible galaxy).

• /etc/ansible/roles is the default location where ansible searches for the roles.

To search for an existing role

ansible-galaxy search <roleName>.   -> will search for role in ansible galaxy.

To install an existing role

ansible-galaxy install <roleName>.   -> will install role from ansible galaxy.

To Create a Role

ansible-galaxy init <roleName>.   -> will create a directory structure as required for a new role.