What is Ansible
Ansible interacting with machines via SSH. So nothing need to be installed in client machines. Only prerequisite is ansible need to be installed in controller machine with python and ssh enabled.
Inventory:
Inventory file:
Inventory file is an simple text file which contains List of machines going to interact with it. We can mention single machines or group of machines going to use it. We can pass direct commands to modules in cmd line using ansible cli.
Cmd: ansible group-name -i <inventory-filename> -m <module-name> <module-params>
ansible group-name -i <inventory-filename> -m <module-name> <module-params>
server1.mycomp.com
server2.mycomp.com
[clients] #group name
server3.mycomp.com
server4.mycomp.com
Ex:
ansible clients -i inventory -m ping
ansible clients -i inventory -m apt -a "name=mysql-server state=present"
Inventory file can also be an executable file. For example if you don’t know the number of instances running in AWS means we can simple write a script to return running instances name from AWS.
Ansible play books:
Ansible playbook is an simple YAML file which contains list of tasks that need to be performed in client machines which we mentioned in inventory file.
playbook.yaml
---
- hosts: all
tasks:
- name: updating package list
apt: update_cache=yes cache_valid_time=3600
- hosts: clients
tasks:
- name: installing mysql server
apt: name=mysql-server state=present
In above code snippet, we used apt module for updating and installing packages. Host all specifies perform the task to all the host machines which we mentioned in inventory file.
And also we can perform task to specific group of hosts. “hosts: client” specifies perform below mentioned tasks only to client group which we created in inventory file. “-name” of each tasks contains some human readable message which will print while performing the tasks. This will be very helpful while monitoring the execution
Running playbook:
ansible-playbook -i inventory playbook.yaml
Vaiables in playbook:
Ansible using jinja2 templating system for dealing with varibles.
playbook.yaml
---
- hosts: all
tasks:
- name: updating package list
apt: update_cache=yes cache_valid_time=3600
- hosts: clients
vars:
init_script: "create_db.sql"
tasks:
- name: installing mysql server
apt: name=mysql-server state=present
- name: coping init sql files
copy: src=/tmp/{{init_script}} dest=/tmp/mysql/{{init_script}}
Variable loops in playbook:
playbook.yaml
---
- hosts: all
tasks:
- name: updating package list
apt: update_cache=yes cache_valid_time=3600
- hosts: clients
vars:
init_script: “create_db.sql"
tasks:
- name: installing mysql server
apt: name={{item}} state=present
with_items:
- python
- python-pip
- vim
- name: coping init sql files
copy: src=/tmp/{{init_script}} dest=/tmp/mysql/{{init_script}}
Other way - we can combine the variables based on hosts vise
playbook.yaml
---
- hosts: all
tasks:
- name: updating package list
apt: update_cache=yes cache_valid_time=3600
- hosts: clients
vars:
packages:
- python
- python-pip
- vim
tasks:
- name: installing mysql server
apt: name={{item}} state=present
with_items: {{packages}}
- name: coping init sql files
copy: src=/tmp/{{init_script}} dest=/tmp/mysql/{{init_script}}
Directory Group variables:
In default ansible will look directory called “group_vars” and “host_vars” in same location which playbook located. If you define any variables under the group_vars directory it will automatically applied to that specific group.
My folder structure:
- inventory
- playbook.yml
- group_vars
- all
- clients
- host_vars
In above folder structure, variable defined in the file called “all” under the group_vars directory which will be available for all hosts defined in inventory hosts. If you want to define variables for specific host create file with same hostname under the “host_vars” directory.
Inventory directory:
Normally inventory file will be simple test file but it can also be an directory.
ansible-playbook -i <inventory-dirctory> playbook.yml
ansible-playbook -i uat deploy.yml
ansible-playbook -i dev deploy.yml
ansible-playbook -i prod deploy.yml
Directory structure of inventory folder:
dev
- hosts
- group_vars
- host_vars
uat
- hosts
- group_vars
- host_vars
Prod
- hosts
- group_vars
- host_vars
deploy.yml
Is there any text files available in your inventory directory, ansible will treat it as inventory file.
Roles in ansible:
You can use single playbook file for managing entire tasks of your infrastructure. But once in a stage your playbook file will be more bigger and hard to manage. For this ansible has the “role” feature, so you can split your playbook yaml file into more moduler way.
You can create a directory called “roles” and create playbook modules.
Roles directory structure:
dev
- hosts
- group_vars
- host_vars
roles
- common
- defaults
- main.yml # variable values
- tasks
- main.yml # list of tasks need to be execute
- files
- server.py # file need to be copy
- templates
- config.py.j2 # template file used for template module
- meta
- main.yml # list the dependency task before perform
- webserver
- defaults
- main.yml # variable values
- tasks
- main.yml # list of tasks
- db
- tasks
- main.yml # list of tasks
deploy.yml
Deploy.yaml
- hosts: database-server
roles:
- common
- db
- hosts: web-server
roles:
Here we can break down the roles folder into more modules. It has documented in ansible documentation site.
Defaults folder contains the variable need to be register
Task folder contains task need to be perform for that group
Files folder contains the files need to be transferred
Templates folder is for template module
Meta folder contains the dependency list for That specific group
Ex:
main.yml
---
Dependencies:
- common
- db
