ansible basics for beginners

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>

 

Inventory:

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

            - server.com

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:


    - common


    - webserver

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