Ansible Basics

basic_ansible.md

Ansible

Ansible is used for automation.

In this post we will learn some basic stuff and workarounds in ansible.

Here is a sample ansible playbook:

hosts: localhost
vars_files:
  - ./vars/main.yml
tasks:
  - name: This a task
    vars: 
      a: "apple"
      b: ["book", "cat", "dog"]
    command: echo "{{ a }}"
    register: sample_task
  - debug: var=sample_task # or msg="{{ sample_task }}"

Basic Commands:

hosts

---

This command contains a list or a environment where all the tasks will run. Hosts can be defined in multiple ways. Like using a custom inventory file, using default inventory file and directly writing after hosts module.

• Directly Writing after hosts module hosts: localhost
• using inventory file Create an inventory file with name inventory with following containts:

[host1]
IP_1
[host2]
IP_2
[host3]
IP_3
[host_list:children]
host1
host2
host3

Write hosts module as: hosts: host1:host2:host3 or hosts: host1 or hosts: hostlist

To exucute playbook use command: ansible-playbook -i inventory my_playbook.yml --private-key="KEY"

• using default inventory Default inventory file is at /etc/ansible/hosts. If inventory file is not provided, this is used as inventory.

tasks

---

This command is used to write tasks to be executed on the environmet, all tasks will be inside this only, for that environment. A simple task is written as:

- name: This a task
  vars: 
    a: "apple"
    b: ["book", "cat", "dog"]
  command: echo "{{ a }}"
  register: sample_task

script

---

Script module is used to upload script at the environment and execute the script. script will contain a complete playbook. A sample task with script module:

- script: './files/my_script.yml -i inventory --private-key=keys/KEY.pem'
  args:
    chdir: '/home/ubuntu/scripts' # the inventory file and keys folder will be located here
  register: output

vars_files

---

List of files that contains the varibales needed in the tasks. A typical vars file:

INT_VAR: 12313
STR_VAR: "Apple"

use:

vars_files:
  - ./vars/main.yml

vars

---

This module is used to inialize new variable.

set_fact

---

This module is used to inialize new variable.

lineinfile

---

with_items, with_list, with_dict

---

For Itrating over list etc.

Data Structure in Ansible:

List:

---

vars:
  my_list:
    - 1
    - 2
    - 3

To append more:

vars:
  my_list: []
set_fact: 
  my_list: "{{ my_list }} + [ {{ item }} ]"

Dictonary:

---

vars:
  dict:
    a: "apple"
    b: "book"
    c: "cat"

To append more:

- name: Create and add items to dict
  vars:
    def_val: "asdf"
    dict: {}
  set_fact:
    dict: '{{ dict | combine( { item: def_val } ) }}'
  with_items:
    - 1
    - 2
    - 3

To get values:

- name: Get values
  debug:
    msg: "{{item.key}}: {{ item.value }}"
  with_dict: "{{ dict }}"