How to automate application deployments using Ansible

• Ansible Expects to automate using Playbooks.
• Playbooks is YAML with predefined Structure.

Playbooks Structure

• Hosts: On which nodes defined in Inventory do you want to execute the playbook
• Syntax of Hosts: name value pair

hosts: all

• Remote_user: User which ansible executes your automation.
• Become: Do you want run the playbook using sudo (set Boolean value)

hosts: all
become: yes

• Tasks: list of individual task
• Task: writing some of task properties

hosts: all
become: yes
tasks:
  - name: <value>
    <module_name>:
      <module_param1>: <module_value1>
      ..
      ..
      ..
      <module_paramn>: <module_valuen>
      state: <module supported state> 

• Example Playbook:

- hosts: all
  become: yes
  tasks:
  - name: install git
    package:
      name: git
      state: present
  - name: uninstall git
    package:
      name: git
      state: absent

Simple Scenario: Installing Tree on all the nodes

• Manual Execution:

sudo apt-get update
sudo apt-get install tree -y

Expressing the above Manual Execution in Ansible

1. Inventory: i need a list with ip addresses/dns names(fqdn)
2. Playbook: lets write the basic structure

- hosts: all
  become: yes
  tasks:
    - name: update ubuntu packages 
    - name: install tree

3. Now we need Modules to automate. Lets define modules. Modules are smallest unit of work in Ansible. There are predefined Modules. You can also define custom modules.
4. To automate the activity lets search modules. lets build a google query around this

apt-get update in Ansible

5. Based of results, lets fill the modules in the above playbook

- hosts: all
  become: yes
  tasks:
    - name: update ubuntu packages and install tree
      apt:
        name: tree
        update_cache: yes
        state: present

6. Create an inventory file with ip addresses in each line
7. create a yaml file called as tree-playbook.yml with the following content

- hosts: all
  become: yes
  tasks:
    - name: update ubuntu packages and install tree
      apt:
        name: tree
        update_cache: yes
        state: present

8. Explore ansible-playbook command line by using ansible-playbook --help | less
9. Command to execute in this case is

ansible-playbook -i test-inventory  tree-playbook.yml

Module Categories In Ansible

• Refer Here for Ansible Module Categories

Execution in Ansible

• Two possibilities:
  • Playbook:
    • Must if you are automating and also if it is frequent activity
    • Can execute multiple modules from one playbook file
  • Adhoc-Commands:
    • Infrequently used activities use adhoc commands.
    • Can execute only one module per command.

Adhoc Commands in Ansible

• Refer Here for complete documentation.
• Syntax:

ansible --help

ansible -i <inventory path> -m <modulename> -a "param1=value1 .. .. paramn=valuen" [-b] <all>

Playbook in Ansible

• Collection of Plays.
• Each play

- hosts: all
  become: yes
  tasks:
    ..
    ..
- hosts: all
  tasks:
    ..
    ..
    

• Each Play in a playbook defines the phase/kind of activities. Generally playbooks are divided into following plays as best practice
  • PRE-DEPLOYMENT: Installing necessary Software’s
  • DEPLOYMENT: Deploying the newly built package to the server
  • POST-DEPLOYMENT: Mostly cleanup activites
• Ansible modules like command, bash, shell etc.. are not idempotent.
• Any module which directly executes os commands is not idempotent and it is not recommended to use these modules until you have no other options.
• If you are using this module, idempotance is your responsibility.