Devops Ansible Tool

What is Ansible?

 Ansible is a free “configuration management” tool.
 Use cases:

•  It’s what you use when you’re tired of copying commands by hand from UNIX tutorials into terminal windows. (Or)
• When you want to set up identical servers that are actually identical.

Why it is required?

Problem # 1:

• When you want to execute series of commands on multiple servers.
• When we try to execute these commands manually by hand. While doing , if you miss any commands which may causes the different issues. 

 Problem # 2:

• Another common problem with managing multiple servers is keeping their configurations identical (or similar)
• When you set up a server (say server1), you tweak the configuration by hand and when you set up another server (server2) you do the same. But then there’s this setting you need to change on server2, which you then forget to change on server1. A different ecosystem was born.

                                               Simple Solution is use Ansible.
Ansible which does the automation or orchestration which makes life of the admin easy. 

Why Ansible is preferred than Puppet, Chef or Salt?

         Ansible uses just SSH ( no overhead of Agents or Agent less)

• The main difference between the other tools and Anisble, is that underneath Ansible is just SSH. Chef and Puppet both have dependencies that must be installed on the server before you can use them, Ansible does not. 
• It runs on your machine and uses SSH to connect to the servers and run the required commands.
• Ansible is agentless uses the PUSH technology. Whereas Puppet, chef needs to have agents to be installed on servers and uses the PULL technology.

Good nice article:[ Source :https://wiredcraft.com/blog/getting-started-with-ansible-in-5-minutes/]




From the above figure,

• Chef or Puppet work by installing an agent on the hosts they manage. This agent is pulling changes from a master host, using their own channel (usually not SSH).  
• Whereas Ansible on the other hand is simply using SSH to push changes from wherever it runs (a server or your own laptop).

Why not just use Bash script rather than Ansible? 

•  Ansible has an edge over Bash scripts because of its simplicity.
•  Ansible just uses a list of tasks to run in YAML format. 
•  Ansible also comes with idempotency out of the box.   That means you can run the same operation numerous times, and the output will remain consistent ( i.e. it won't do something twice unless you ask it to). You can write Bash scripts this way, but it requires quite a bit more overhead

Basic terms of Ansible:

PLAYBOOK:  

• In ansible, a definition of how a server should look  is called a playbook. 
• In a playbook, you define what actions ansible should take to get the server in the state you want. Only what you define gets done. (or)
• Ansible playbook is just a series of tasks that are performed in sequence, and a simple sequence fits entirely in one file

 YAML : YAML stands for "YAML Ain't Markup Language"

• (rhymes with camel) is a human-readable data serialization language. It is commonly used for configuration files [ Source from Wiki]
• Playbook are written in YAML language.
• YAML is not programming language and it is easy to write the .yml files.   e.g: first-playbook.yml
• YAML files should end in .yaml whenever possible.
• YAML is case sensitive.
• YAML does not allow the use of tabs. Spaces are used instead as tabs are not universally supported.

YAML Basic Data Types

•  Mappings (hashes / dictionaries), 
•   Sequences (arrays / lists), and  
•   Scalars (strings / numbers). 

Lists:
All members of a list are lines beginning at the same indentation level starting with a "- " (a dash and a space)

---
# A list of tasty fruits
fruits:
    - Apple
    - Orange
    - Strawberry
    - Mango
...

 Mappings (hashes / dictionaries)

 A dictionary is represented in a simple key: value form (the colon must be followed by a space):

# An employee record
martin:
    name: Martin D'vloper
    job: Developer
    skill: Elite

 More complicated data structures are possible, such as lists of dictionaries, dictionaries whose values are lists or a mix of both:

# Employee records
-  martin:
    name: Martin D'vloper
    job: Developer
    skills:
      - python
      - perl
      - pascal
-  tabitha:
    name: Tabitha Bitumen
    job: Developer
    skills:
      - lisp
      - fortran
      - erlang

Dictionaries and lists can also be represented in an abbreviated form if you really want to:

---
martin: {name: Martin D'vloper, job: Developer, skill: Elite}
fruits: ['Apple', 'Orange', 'Strawberry', 'Mango'] 

Scalars (strings / numbers):
They are the strings and numbers that make up the data on the page. A scalar could be a boolean property, like Yes, integer (number) such as 5, or a string of text, like a sentence or the title of your website. Scalars are often called variables in programming

integer: 25
string: "25"
float: 25.0
boolean: Yes 

property, like Yes, integer (number) such as 5, or a string of text, like a sentence or the title of your website.

Task  [Source: http://abregman.com/2015/12/25/ansible-write-and-run-your-first-playbook/]

A task  is simply the use of one of Ansible modules. Module implements specific functionality.  

For example, installing package would be task since it will require us to use the ‘apt’ module. 

There many modules, so task can be running service, fetching files, adding user and many more modules waiting for you to explore. 

- name: Ensure apache2 is installed

  apt: name=apache2 state=present

In the above example

• we use apt module to install package named ‘apache2’. The state is the action we are using on this package.so ‘present’ tells Ansible to make sure apache2 installed in the system. 
• There are additional states, as ‘latest’ which means ‘make sure latest package is installed’.

What is play in Ansible?

Play is a collection of tasks running against one or more hosts. It includes one or more task.

What is playbook?

Playbook composed of one or more plays.

Now, let us learn how to use the ANSIBLE in practical application.

Step 1: How to install Ansible in Ubuntu Linux machine?

Step 2: How to setup the hosts in /etc/hosts/ansible? 

Step 3: How to write the playbook?

Step 4: How to run the playbook using ansible commands?

How to install Ansible in Ubuntu Linux machine?

To run ansible, you need Python 2.6 or higher on the machine you run ansible from. Most current operating systems have this by default. 

sudo apt-add-repository -y ppa:ansible/ansible

sudo apt-get update

sudo apt-get install -y ansible

The easiest way to install these is to use pip. Let’s first install pip for your distribution.

    sudo apt-get install python-pip python-dev

    sudo pip install ansible

How to setup the hosts in /etc/ansible/hosts? 

Next step is Setup inventory or Manage servers or Setup Hosts in /etc/ansible/hosts file.

If the above file doesn't exists then create it using the below commands

   (sudo) mkdir /etc/ansible

   (sudo) touch /etc/ansible/hosts

else  Edit the /etc/ansible/hosts

Let’s say you have two nodes, named hostA and hostB. You can  simply add these two lines to ‘/etc/ansible/hosts

   hostA

   hostB

   [Group_Webservers]

   192.168.1.0

   192.168.2.0

   

   [my_group_of_hosts]

   hostA

   hostB

Define a group called as ‘Group_Webservers’. A group can be used in a playbook to run the playbook against a number of hosts. We’ve  added two hosts to the group (Group_Webservers). 

Source from : [http://abregman.com/2015/12/25/ansible-write-and-run-your-first-playbook/]

How to write the playbook? 

Now learn about writing playbook. Let's start play with the cool example.

So imagine our environment consists of two hosts:  hostA and hostB

We want to have two plays:

First play: one simple task – create file in /tmp named ‘apple_file’.

Second play: two tasks  – task to add user named ‘muni’ with bash as default shell, and another task to install the latest  ‘python’ package.

We know what we want to run and on what hosts we want to run it. Let’s start with the first play:

---

- hosts: hostB
  tasks:
      - name: Create file
        file: path=/tmp/apple_file state=touch

– hosts: hostB tells Ansible on which nodes to run the task in the above playbook. Here we mentioned as hostB, on which these task runs.

tasks: is a list of tasks, each using one of the available modules of Ansible that you would like to execute on remote hosts. In our case, hostB.

Our list contain only one task that uses ‘file’ module. ‘file’ module allows us to create/remove files and directories or modify their attributes. In the example above we simply create empty file. the ‘path=/tmp/apple_file’ used by the module to to create ‘apple_file’ file in /tmp dir. by “state=touch” we are actually telling Ansible we would like to ensure such file exists. If it exists, ansible will do nothing, but if it doesn’t, it will create it.

Let's extend the playbook,

---
- hosts: hostB
  tasks:
      - name: Create file
        file: path=/tmp/apple_file state=touch

- hosts: my_group_of_hosts
  sudo: yes
  tasks:
      - name: Create user
        user: name=muni shell=/bin/bash

      - name: Install python
        apt: name=python state=latest

   

We now have two plays. How do we know that? We can see end of tasks list of our firs play and you can notice a start of new play by the line that starts with “-hosts …’.

There are two tasks – First one is for creating new user. We used the ‘user’ module for that. We wanted him to have bash as default shell? that is the ‘shell=/bin/bash’.

Second task is about installing new package in your system. It using the ‘apt’ module with two options – name  of the package to be installed and state=latest. In the first example, we used ‘state=present’ to simply have the package installed in our system. ‘state=latest’ makes sure that if there is newer package available, it will be installed.

There is the ‘sudo: yes”. While for the first play you didn’t have to be root, because every user can create files in ‘/tmp’, for the second play you must be. Not every user can create new users in the system. So we ran the second play with sudo to make sure the play will not fail due to lack of permissions.

Below, you can find more examples about the Playbooks.

How to run the playbook using ansible commands

The command for running playbooks is pretty straightforward:

ansible-playbook <playbook name>

PLAY [hostB] ******************************************************************

GATHERING FACTS ***************************************************************
ok: [hostB]

TASK: [Create file] ***********************************************************
changed: [hostB]

PLAY [my_group_of_hosts] ***************************************************************

GATHERING FACTS ***************************************************************
ok: [hostA]
ok: [hostB]

TASK: [Create user] ***********************************************************
changed: [hostA]
changed: [hostB]

TASK: [Install python] **********************************************************
ok: [hostA]
ok: [hostB]

PLAY RECAP ********************************************************************
hostA                      : ok=5    changed=2    unreachable=0    failed=0
hostB                     : ok=3    changed=1    unreachable=0    failed=0

   

‘GATHERING FACTS’  is a step in which Ansible gather all kind of information about your remote system (memory, os distribution, ip addresses, etc). To see what information gathered in this step you can use:                                         

                                               ansible -m setup <hostname>