YAML:
stands for Yet Another Mark up language.
- is a data serialization language designed to be readable and writable by humans
- it is commonly used for configuration files but it is used in many apps where data being stored and transmitted over the network.
- We can communicate with another language too by using Yaml including OS and or services/apps running on OS.
- Yaml is case sensitive scripting language
- In Yaml , it doen't allow Tabs for indentation , you have to use spaces instead
Keys:
Key is used to store any value and that can be changed depending on condition in any other language.
For ex: x: 10
Sequence data collection:
this is same as array in another language , like list of same data type values. We can represent as below
sequence representation
name:
- value1
- value2
Here name is array name, value1, value2 are items of array.
you can also represent as below
name: [value1,value2]
Map Data collection
It is same definition as in Java
Map representation
family:
krishh: 20
ram: 10
you can also add sequence data inside Maps as below
family:
krishh: 20
sachin: 45
- fullname: Ramesh Sachin Tendulkar
- age: 50
- score: 2000
rohit: 40
Dhawan: 46
sequences are ordered collections and Maps are unordered collections
Ansible Play book
Playbook is used to send commands to remote servers / execute commands in remote servers in a scripted way using ansible commands.
To understand playbooks we need to know the below.
- Task
- Install tomcat in remote server
- Play
- collection of tasks is called Play
- Install java
- Install tomcat
- create file in home directory
- playbook
- collection of Plays
- it a combination of Play and Tasks.
- Here we can write plays for one server or multiple servers.
- Playbooks
- More than one play book means more than one yml file you are writing for your requirement.
How to write Ansible playbook
- start with --- (3 - ) at the start of the yml file , it means that you are writing yml file.
- Target section list (hosts,users etc)
- variables list (optional)
- Tasklist
- list all the modules that you run in the order
These are the steps we need to write in yaml or yml file and we call it this for one play.
Sample.yml
Yaml file contains sequences and each sequence is called one play.
If you are writing playbook for Ansible , hosts is the default key , where you are providing servers group name.
How to write yaml sccript
first.yml : write this yml file in ansible server
---
- hosts: ansible-servers
vars:
mycontent: "this file is created using var content"
tasks:
- copy:
dest: /tmp/var_file.txt
content: "{{ mycontent }}"
execute this command in ansible server:
ansible-playbook first.yml
Now open ansible host and check for file in the location : /tmp/var_file.txt.
It will be created as below
else you can execute below command to check without manually opening the file in client
ansible ansible-servers -m command -a "cat /tmp/var_file.txt ".
So that you can see the below content for the same.
Reading vars from command line using vars_prompt
Write yml file as below to test this.
read.yml
---
- name: this is play1
hosts: localhost
vars_prompt:
name: var1
prompt: enter any value ?
and execute yml file : ansible-playbook read.yml
Note: the value which you are entering will be assigned to the variable which is in yml file.
Print variable value using command line
For this use debug module in playbook, debug module has one argument as msg.
read.yml
---
- name: this is play1
hosts: localhost
vars_prompt:
name: var1
prompt: enter any value ?
tasks:
- name: "this is to print the variable value"
debug:
msg: "this is the value you entered {{ var1 }} "
output as below
suppose if you are not assigning or entering any value , default value it set as "Hello world".
Using loops:
Lets see an example without loops , how we need to create 3 siilar directories by using command and name in yml
---
hosts: localhost
tasks:
- name: this will create dir1
command: mkdir /tmp/dir1
- name: this will create dir2
command: mkdir /tmp/dir2
- name: this will create dir3
command: mkdir /tmp/dir3
once you execute above yml file, it will create 3 dirs under tmp folder,.
instead of executing same command multiple times, we can use loops concept here for easy purpose.
---
- hosts: ansible-servers
tasks:
- name: this is to create dirs
command: mkdir /tmp/"{{ item }}"
with_items:
- new_dir1
- new_dir2
- new_dir3
output in /tmp of ansible client server after executing above playbook
Now , lets see how we can pass variable while running playbook and set those varaible values inside if your plabook
ansible-playbook read.yml -e "var1= hi var2=bye "
---
- name: this is a play
hosts: localhost
- tasks:
- debug:
msg: "the value of var1= {{ var1 } } and var2={{ var2 }} "
When you execute above script , it will assign values what you entered.
Conditional statements :
Use when keyword to give a condition to execute.
when above file executed , when_file.txt will be created , if you make when: false , it won't be created.
Yaml modules: deligate_to and register
register:
module is used to store the response to a variable after completion of each task.
if you want to store the response of each task after completion , we can use register at the end of the task.
this module is very helpful in conditional statements.
---
- name: This is a play
hosts: ansible-servers
tasks:
- command: touch /tmp/register_module.txt
register: response_out
- debug:
msg: "{{response_out}}"
output :
This module will help us in executing task only servers/hosts which are given as parameter to delegate_to parameter .
for ex:
---
- name: This is a play
hosts: ansible-servers
tasks:
- command: touch /tmp/register_module.txt
delegate_to: localhost
here though you pass hosts: ansible-servers , the file won't create here instead of that it will create in localhost or the server which you given an argument to delegate_to.
Ansible Playbook to install vim and wget on client machines.
---
- hosts: ansible-servers
become: yes
tasks:
- yum:
name: wget
state: present
- yum:
name: vim
state: present
Ansible automation is designed to fulfil the below requirements
- provisioning
- configuration
- application deployment
- orchestration
