Features of Ansible

Ansible is Modular
1000+ Modules available.
Modules written in python.

Running Ansible

Do not use Root account for ansible
Create an account with all privileges:

sudo visudo
%ansible ALL=(ALL)    ALL

usermod -aG ansible aman

Install python on all hosts:

yum install -y python2 epel-release

Add entry to Hosts file & enable key less SSH access:

ssh-copy-id -i ~/.ssh/id_rsa.pub aman@server2

Using the same username is convenient but not required.

Inventory file

cd install
nano inventory

[all]
controller.example.com
node1.example.com

[servers]
node1.example.com
server1.example.com

ansible all -i inventory --list-hosts

Ansible Config File

Variour ansible.cfg files:

/etc/ansible/ansible.cfg
~/.ansible.cfg
ansible.cfg in project directory (takes precedence)

Contents:

become:           Specify how to escalate privileges on the managed host.
become_user:      Specify which user account to use on remote host.
become_ask_pass:  Whether or not a password should be asked.
inventory:        Which Inventory files to be used.
remote_user:      Name of user account on the managed host. Not set by default, so local username is used.

Privilege Escalation

Ansible runs tasks on managed host using same user account as local user, so make sure to copy ssh keys.
Set remote_user in ansible.cfg to specify another user to be used.
If remote_user is not specified, Privilege Escalation can be used.
Enable in [privilege_escalation] section in ansible.cfg:
  become=True
  become_method=sudo
  become_user=root
  become_ask_pass=False
Privilege escalation needs sudo configuration
Create a sudo file on all Ansible managed hosts:
  nano /etc/sudoers.d/user
  user ALL=(ALL) NOPASSWD: ALL

Adhoc Commands

Used for Diagnostics like querying a large number of hosts.
To quickly make changes to many managed hosts
Modules are used:

-m    Specifies Modules 
-a    Specifies Arguments

Default Module can be set in ansible.cfg file.
3 Adhoc commands:

command:  runs command on managed host
shell:    runs command on managed host through the local shell
copy:     copy a file, change content on a remote host in a target file

ansible all -i inventory -m command -a id
ansible all -i inventory -m command -a id -o
ansible all -i inventory -m command -a env
ansible all -i inventory -m shell -a env
ansible server1 -m copy -a 'content="Ansible Managed\n" dest=/etc/motd'

Modules

List Modules:

ansible-doc -l

Module Help:

ansible-doc <modulesname>

Create sample config:

ansible-doc -s <modulesname>

Using Modules:

ansible all -i inventory -m ping
ansible -i inventory -m ping all

Using in Playbooks:

tasks:
- name: Install a package
  yum: 
     name: vsftpd
     state: latest

YAML

YAML(YAML Ain't Markup Language) structures are represented by indentation.
Data elements at same hierarchy level should be at same indentation level.
Do not use Tabs for indentation.
It is common but not mandatory to start YAML file with 3 dashes & end it with 3 dots.
This allows YAML code to be placed in some other code.

Example:

---
# example playbook
item1:
  parameter1
  parameter2
    option1
    option2
item2
  parameter3
...

YAML Contents

Dictionary: key/value pair written in key: value notation
Lists: represent a list of items, enumerated as - item. Space after - is mandatory.
Strings can be enclosed in single or double quotes but that is not mandatory.
In a multi-line string, first line is ended by | or >. Next lines are indented.
Verify YAML syntax:

ansible-playbook --syntax-check mycode.yaml

Dry Run:

ansible-playbook -C mycode.yaml

Step-by-Step:

ansible-playbook --step mycode.yaml

Playbook

Tasks are performed by Modules.
Ordering is important: Plays & Tasks are executed in the order they are presented.
Playbooks do not change anything if the host is already in desired state.
Avoid modules like command, shell & raw as they are not idempotent by nature.

Task Attribute

Most important Attribute is Task attribute:

tasks:
- name: run service
  service: name=vsftpd enabled=true

Here '-' marks beginning of a list of attributes.
If multiple tasks are defined, each first attribute of task starts with '-'.

Other Attributes

name:  specify a specific label to play
hosts: uses patterns to define on which hosts to run a play
remote_user: overwrites the remote_user setting in ansible.cfg
become: overwrites the become setting in ansible.cfg
become_method: overwrites the become_method setting in ansible.cfg
become_user: overwrites the become_user setting in ansible.cfg

Variables

Used for repeated tasks like:

Creating users
Removing files
Installing packages

Names must start with letters
Can be defined at a lot of levels
Can be defined with different scope:

Global Scope: Set from CLI or ansible configuration file
Play Scope: Defined in playbook
Host Scope: Set on groups or Individual hosts through inventory file.

Variables defined at highest level wins: Global scope wins from host scope

Defining Variables

Defining in Playbook:

- hosts: all
  vars:
    user: test
    home: /home/test

Using variable files:

- hosts: all
  vars_files:
    - vars/users.yml

$ cat vars/users.yml
user: test
home: /home/test
user: test2
home: /home/test2

Using Variables

tasks:
  - name: Creates the user {{user}}
    user:
      name: "{{ user }}"

Host and Group Variables

Host Variable:  Applies to one host defined in Inventory file.
Group Variable: Applies to multiple hosts defined in Inventory file.

Depricated method: Define them in Inventory file:

[webservers]
webserver.example.com
[webservers:vars]
user=test

Recommended method: Use group_vars & host_vars directories in project directory which contains inventory file.

nano group_vars/webservers
nano host_vars/server01

Variables can be overwritten from CLI using

ansible-playbook -e "key=value"

Arrays

Define multiple values
Refer to these using: users.test.first_name

users:

 test:
   first_name: test
   last_name: done
   home_dir: /home/test
 test2:
   first_name: test2
   last_name: done
   home_dir: /home/test2

Facts

Contain discovered information about a host
Can be used in conditional statements to make sure certain tasks run only if they are necessary.
Setup module is used to gather fact information

ansible -i inventory servers -m setup

Facts provide a lot of information, Filter them:

ansible -i inventory servers -m setup -a 'filter=ansible_kernel'

Custom facts can be created to display information about a host.
Create a file on the Managed Host:

sudo nano /etc/ansible/facts.d/servers.fact
 [server_info]
 profile = web_server

Check the facts:

 ansible -i inventory servers -m setup -a 'filter=ansible_local'

Inclusions

These make it easy to create a modular Ansible Setup.
Main variables can be set in the master Ansible file, generic tasks can be defined in included files.
Tasks can be included in a playbook from external YAML file using include directive.
Variables can be included from YAML or JSON file using include_vars directive.