Templates and Files

Managing configuration files is one of the most common tasks in infrastructure automation. Ansible provides the template module (powered by Jinja2) for dynamic files and the copy module for static files.

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Static Files vs Templates

Feature	copy Module	template Module
Source	Static file	Jinja2 template (.j2)
Variables	Not supported	Fully supported
Logic	None	Conditionals, loops, filters
Use case	Files that never change	Configuration files that vary per host or environment

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The copy Module

Copy static files from the control node to managed nodes:

tasks:
  - name: Copy static HTML file
    copy:
      src: files/index.html
      dest: /var/www/html/index.html
      owner: www-data
      group: www-data
      mode: '0644'

  - name: Copy with backup
    copy:
      src: files/app.conf
      dest: /etc/app/app.conf
      backup: true    # Create a backup of the existing file

Important copy Parameters

Parameter	Description
src	Source file on the control node
dest	Destination path on the managed node
owner	File owner
group	File group
mode	File permissions (e.g., '0644')
backup	Create a backup before overwriting
content	Write inline content instead of copying a file
validate	Command to validate the file before placing it

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Jinja2 Template Basics

Jinja2 is the templating engine used by Ansible. Templates use the .j2 extension by convention.

Syntax Elements

Syntax	Purpose	Example
{{ }}	Variable output	{{ ansible_hostname }}
{% %}	Logic (if, for, etc.)	{% if env == 'prod' %}
{# #}	Comments	{# This is a comment #}

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The template Module

tasks:
  - name: Deploy nginx configuration
    template:
      src: templates/nginx.conf.j2
      dest: /etc/nginx/nginx.conf
      owner: root
      group: root
      mode: '0644'
      validate: "nginx -t -c %s"
    notify: Restart nginx

Important template Parameters

Parameter	Description
src	Source Jinja2 template on the control node
dest	Destination path on the managed node
owner	File owner
group	File group
mode	File permissions
validate	Command to validate the rendered file (use %s for the file path)
backup	Create a backup before overwriting

Tip: The validate parameter is extremely useful for configuration files --- Ansible will only deploy the file if validation passes.

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Template Examples

Simple Variable Substitution

templates/nginx.conf.j2:

worker_processes {{ nginx_worker_processes | default('auto') }};

events {
    worker_connections {{ nginx_worker_connections | default(1024) }};
}

http {
    server {
        listen {{ nginx_port }};
        server_name {{ nginx_server_name }};
        root {{ nginx_root }};
    }
}

Conditionals

{% if env == 'production' %}
log_level = warn
debug = false
{% elif env == 'staging' %}
log_level = info
debug = false
{% else %}
log_level = debug
debug = true
{% endif %}

Loops