Ansible Cheat Sheet – A DevOps Quick Start Guide

Ansible uses SSH to communicate between the nodes.

To set up an SSH connection, follow the steps mentioned below:

• Setting Up SSH Command
• Generating SSH Key
• Copy the SSH Key on the Hosts
• Check the SSH Connection

#Setting Up SSH Command
$ sudo apt-get install openssh-server

#Generating SSH Key 
$ ssh-keygen

#Copy the SSH Key on the Hosts
$ ssh-copy-id hostname

#Check the SSH Connection 
$ ssh <nodeName>

To install Ansible in Debian based Linux, you can follow the following steps:

• Add the Ansible repository to your system, before installing Ansible
• Then run the update command before installing, to update the existing packages 
• After that install the Ansible package 

#Add Ansible repository 
$ sudo apt-add-repository ppa:ansible/ansible

#Run the update command 
$ sudo apt-get update

#Install Ansible package 
$ sudo apt-get install ansible

#Check Ansible Version
$ ansible –version

The inventory file of Ansible lists all the platforms you want to automate across. Ansible at a single instance can work on multiple hosts in the infrastructure. It is also possible to have multiple inventory files at the same time.

• The host inventory file can contain hostnames either individually or in groups
• Host Groups can be created by giving a group name within square brackets
• Group members can then be listed under, till there is a line break

Below is an example inventory file, which you can refer to understand the various parameters.

#Default location for host file
$ /etc/ansible/hosts

#To define location for inventory, in CLI
-i<path>

#example host file

ungrouped.example.com                                     #An ungrouped host

[webservers]                                              #a group called webservers
beta.example.com ansible_host = 10.0.0.5                  #ssh to 10.0.0.5
github.example.com ansible_ssh_user = abc                 #ssh as user abc

[clouds]
cloud.example.com fileuser = alice                        #fileuser is a host variable

[moscow]
beta.example.com                                          #host (DNS will resolve)
telecom.example.com                                       #host(DNS will resolve)

[dev1:children]                                           #dev1 is a group containing
webservers                                                #all hosts in group webservers
clouds                                                    #all hosts in group clouds

Ad-Hoc commands are quick commands which are used to perform the actions, that won’t be saved for later.

Some of the tasks that you can perform using Adhoc commands are as follows:

• Parallelism and Shell Commands
• File Transfer
• Managing Packages
• Deploying From Source Control
• Managing Services

I am going to explain all these tasks, with a basic example.

Basic Example: To reboot all the web servers present in Europe, 20 at a time.

Playbooks in Ansible are written in YAML format. It is a human-readable data serialization language that is commonly used for configuration files. It can also be used in many applications where data is being stored.

A playbook has various parameters that you need to mention, like Hosts & Users, Variables, Tasks, Handlers, Modules and Return Values.

This is the sample playbook to start the Apache httpd Server program. 

#Every YAML file starts with ---
---
- hosts: webservers
  vars:
    http_port: 80
    max_clients: 200
  remote_user: root

  tasks:
  - name: ensure apache is at the latest version
    apt: name=httpd state=latest
  - name: write the apache config file
    template: src=/srv/httpd.j2 dest=/etc/httpd.conf
    notify:
    - restart apache
  - name: ensure apache is running (and enable it at boot)
    service: name=httpd state=started enabled=yes

  handlers:
    - name: restart apache
      service: name=httpd state=restarted

Follow the below steps to write a run a playbook. For the ease of understanding, the commands are in a generalized format.

#SSH Key Generation
$ ssh key-gen

#Copy the  generated public SSH key on your hosts
$ ssh-copy-id -i root@<IP address of your host>

# List the IP addresses of your hosts/nodes in your inventory 
$ vi /etc/ansible/hosts

#Ping to ensure a connection has been established
$ ansible -m ping <Name of the Host>

#You do not have to follow the above steps, if you already have host connected to the control machine.

#Create a Playbook
$ vi <name of your file>.yml

#To write the playbook refer to the snapshot here.

#Run the playbook
$ ansible-playbook <name of your file>.yml