Ansible Template Variables Tutorial

Introduction

In Ansible, templates are files that contain variables and are used to dynamically generate configuration files, scripts, or other text-based files. Template variables allow for the customization of these files based on the needs of your infrastructure.

What Are Template Variables?

Template variables in Ansible are placeholders within a template file that are replaced with actual values when the template is processed. These variables are defined in your Ansible playbooks or inventory files.

Defining Template Variables

You can define variables in several ways in Ansible:

• In the inventory file
• In playbooks
• As facts gathered by Ansible

Here's an example of defining variables in a playbook:

---
- name: Example Playbook
  hosts: all
  vars:
    my_var: "Hello, World!"
  tasks:
    - name: Debug variable
      debug:
        msg: "{{ my_var }}"
                

Creating a Template File

Template files in Ansible use the Jinja2 templating engine. A template file typically has the .j2 extension. Here's an example of a simple template file:

# template.j2
Welcome to {{ my_var }}!
                

Using the Template Module

To apply a template file in your playbook, you use the template module. Here's an example playbook that uses the template module:

---
- name: Apply Template Example
  hosts: all
  vars:
    my_var: "Ansible"
  tasks:
    - name: Copy template file
      template:
        src: template.j2
        dest: /tmp/template_output.txt
                

This playbook will replace the {{ my_var }} placeholder in template.j2 with the value "Ansible" and copy the rendered file to /tmp/template_output.txt.

Rendering the Template

When the playbook is run, the template is rendered with the variable values. The content of /tmp/template_output.txt would be:

Complex Variables

Template variables can also be more complex data structures like dictionaries and lists. Here's an example:

---
- name: Complex Variables Example
  hosts: all
  vars:
    user_info:
      name: John Doe
      email: john.doe@example.com
  tasks:
    - name: Copy complex template
      template:
        src: complex_template.j2
        dest: /tmp/complex_template_output.txt
                

And the corresponding template file complex_template.j2:

# complex_template.j2
User Information:
Name: {{ user_info.name }}
Email: {{ user_info.email }}
                

Conditional Statements

Jinja2 templates also allow for the use of conditional statements. Here's an example:

# conditional_template.j2
{% if user_info.name %}
Hello, {{ user_info.name }}!
{% else %}
Hello, Guest!
{% endif %}
                

This template will greet the user by name if user_info.name is defined, otherwise, it will greet "Guest".

Loops in Templates

You can also use loops in your templates to iterate over lists or dictionaries. Here's an example:

# loop_template.j2
Users:
{% for user in users %}
- {{ user.name }} ({{ user.email }})
{% endfor %}
                

Conclusion

Template variables in Ansible provide a powerful way to dynamically generate files based on the state of your infrastructure. By using the Jinja2 templating engine, you can create complex and flexible templates that adapt to your needs.

With the knowledge of defining variables, creating template files, and using the template module, you can now start leveraging the full potential of templates in Ansible.