How to define use ansible variables?

 Variables in Ansible

Ansible is a powerful automation tool that can be used to manage infrastructure, deploy applications, and orchestrate complex workflows. One of the key features of Ansible is its ability to use variables to define and configure tasks and playbooks. Variables allows to reuse values across different parts of playbook, make code more dynamic, flexible and also allow to create flexible playbooks that can be used across different environments.

In this article, we will explore the different ways that variables can be used in Ansible and provide some example code to illustrate their usage.

Defining Variables

Variables can be defined in several ways in Ansible. The most common method is to use YAML syntax to define variables directly in your playbook. For example:

---------------------------------------------

- name: Deploy web server

  hosts: web_servers

  vars:

    web_port: 80

    app_version: 1.0.0

  tasks:

    - name: Install nginx

      apt:

        name: nginx

        state: present

      become: yes

 

    - name: Configure nginx

      template:

        src: nginx.conf.j2

        dest: /etc/nginx/nginx.conf

        mode: 0644

      become: yes

 

In this example, we define two variables, web_port and app_version, which can be used later in the playbook. The vars section is used to define these variables at the playbook level, but you can also define variables at the task or role level.

Variables are used in the tasks using Jinja2 templating syntax. For example, if we want to use the web_port variable in the nginx.conf.j2 template file, we can do the following:

# nginx.conf.j2

server {

    listen {{ web_port }};

    # ...

 

The curly braces {{ }} indicate that this is a variable that should be replaced with its value at runtime. When the template is rendered, the {{ web_port }} expression will be replaced with the value of the web_port variable.

You can also define variables in external files, which can be useful for separating sensitive information like passwords and API keys from your playbook code. Ansible supports several file formats for variables, including YAML, JSON, and INI. For example, you can define variables in a YAML file like this:

---

# vars.yml

web_port: 80

app_version: 1.0.0

 

You can then include this file in your playbook using the vars_files parameter:

----------------------------------------

---

- name: Deploy web server

  hosts: web_servers

  vars_files:

    - vars.yml

  tasks:

    # ...

 

Using Variables in Tasks

You can define variables within a playbook and use them within tasks. Here's an example playbook that uses variables to install different packages on different hosts:

- name: Install Packages

  hosts:

    - web

    - db

  vars:

    web_packages:

      - httpd

      - mod_ssl

    db_packages:

      - mysql-server

  tasks:

    - name: Install Packages on Web Hosts

      yum:

        name: '{{ web_packages }}'

        state: present

      when: '''web'' in group_names'

    - name: Install Packages on DB Hosts

      yum:

        name: '{{ db_packages }}'

        state: present

      when: '''db'' in group_names'

 

In this playbook, we define two sets of packages for the web and db hosts using variables (web_packages and db_packages). We then use the `when` keyword to ensure that the tasks are only executed on the appropriate hosts.

Using Variables in Templates

You can use variables in templates to create dynamic configuration files. Here's an example playbook that uses a template to create an Apache virtual host configuration file:

------------------------------------

- name: Configure Apache Virtual Host

  hosts: web

  vars:

    server_name: example.com

    docroot: /var/www/html/example

  tasks:

    - name: Create Apache Virtual Host Configuration File

      template:

        src: templates/vhost.conf.j2

        dest: /etc/httpd/conf.d/{{ server_name }}.conf

      notify:

        - restart httpd

 

In this playbook, we define two variables (server_name and docroot) that are used in the template file (vhost.conf.j2) to create the virtual host configuration file. We then use the notify keyword to restart the Apache service when the configuration file is updated.

Using Variables in Roles

Roles are reusable Ansible components that can be used across different playbooks. You can use variables within roles to create flexible and customizable components. Here's an example role that installs and configures the Nginx web server:

---

- name: Install Nginx

  hosts: all

  become: true

  vars:

    nginx_version: 1.20.1

  tasks:

    - name: Install Nginx

      yum:

        name: nginx-{{ nginx_version }}

        state: present

    - name: Configure Nginx

      template:

        src: templates/nginx.conf.j2

        dest: /etc/nginx/nginx.conf

      notify:

        - restart nginx

In this role, we define a variable (nginx_version) that is used to install a specific version of Nginx. We also use a template file (nginx.conf.j2) to create the Nginx configuration file. Finally, we use the notify keyword to restart the Nginx service when the configuration file is updated.

 

You can also use variables in other parts of your tasks, such as command arguments, file paths, and conditional expressions. For example:

- name: Create user account

  user:

    name: "{{ user_name }}"

    password: "{{ hashed_password }}"

    groups: "{{ user_groups }}"

    shell: /bin/bash

    home: "/home/{{ user_name }}"

    state: present

  become: yes

 

- name: Copy config file

  copy:

    src: "{{ app_config_file }}"

    dest: "/etc/myapp/config.yml"

    mode: 0644

  become: yes

 

- name: Stop service if it's running

  service:

    name: myservice

    state: stopped

  when: myservice_state == "running"

 

Overriding Variables

Sometimes you may need to override a variable value for a specific task or host. Ansible provides several ways to do this, including using the --extra-vars command-line option, setting environment variables, or passing variables through inventory files.

For example, you can override the web_port variable for a specific host like this:

---

- name: Deploy web server

  hosts: web_servers

  vars:

    web_port: 80

  tasks:

    - name: Install nginx

      apt:

        name: nginx

        state: present

      become: yes

 

    - name: Configure nginx

      template:

        src: nginx.conf.j2

        dest: /etc/nginx/nginx.conf

        mode: 0644

      become: yes

      vars:

        web_port: 8080

 

 

Conclusion

Variables are a powerful feature of Ansible that allow you to create flexible and customizable playbooks. In this bloga, we provided some examples of how to use variables in tasks, templates, and roles. These examples demonstrate the flexibility and power of Ansible, and how it can be used to automate a wide range of tasks and scenarios.