Stage 4 · Provision

Playbooks & Variables

Jinja2 Templates

Templating config files with filters, loops, and facts.

7 min readAnsible AutomationProvision

The Template Module

The template module copies a Jinja2 template from the control node to managed nodes, rendering variables into the output. Templates live in a templates/ directory alongside your playbook or role.

Using the template module


- name: Deploy nginx config
  template:
    src: nginx.conf.j2
    dest: /etc/nginx/nginx.conf
    owner: root
    group: root
    mode: "0644"
    backup: yes
  notify: Restart nginx

The template module is idempotent — it only reports changed if the rendered content differs from the destination file.

Jinja2 Syntax

Jinja2 uses double curly braces for variable substitution and percent signs for control structures. Ansible templates are Jinja2 with access to all Ansible variables and facts.

templates/nginx.conf.j2


# {{ ansible_managed }}
# This file is managed by Ansible. Do not edit manually.

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

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

http {
    server {
        listen {{ http_port | default(80) }};
        server_name {{ server_name }};

        location / {
            proxy_pass http://127.0.0.1:{{ app_port }};
        }
    }
}

{{ ansible_managed }} is automatically replaced with a comment showing who managed the file and when.

Common Filters

Jinja2 filters transform variables. They are chained with the pipe character. Ansible adds many filters beyond the standard Jinja2 set.

Filter examples


# Default value
{{ nginx_port | default(80) }}

# Uppercase
{{ app_name | upper }}

# JSON formatting
{{ config_dict | to_nice_json }}

# YAML formatting
{{ config_dict | to_nice_yaml }}

# File path basename
{{ '/etc/nginx/nginx.conf' | basename }}

# Combine lists
{{ groups['webservers'] | join(', ') }}

# Hash for cache busting
{{ content | hash('sha256') }}

# Regex replace
{{ hostname | regex_replace('^web', 'app') }}

Filters are powerful for transforming data in templates. Chain them for complex transformations.

Debug filters

Use the debug module with filters to test: ansible all -m debug -a 'msg={{ variable | default("N/A") }}'. This lets you verify filter behavior before adding to templates.

Conditionals in Templates

Conditional template sections


{% if enable_ssl %}
server {
    listen 443 ssl;
    ssl_certificate {{ ssl_cert_path }};
    ssl_key {{ ssl_key_path }};
}
{% else %}
server {
    listen 80;
}
{% endif %}

{% if environment == 'production' %}
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;
{% else %}
access_log /dev/null;
{% endif %}

Conditionals let you customize config files per environment without separate templates for each case.

Loops in Templates

Looping in templates


{# List of upstream servers #}
upstream backend {
{% for server in backend_servers %}
    server {{ server.host }}:{{ server.port }} weight={{ server.weight | default(1) }};
{% endfor %}
}

{# Iterate over dictionary #}
{% for key, value in app_config.items() %}
{{ key }} = {{ value }}
{% endfor %}

Loops generate repeated config sections from variable lists. This eliminates duplication when managing server pools or feature flags.

Whitespace control

Jinja2 whitespace can cause unexpected blank lines. Use {%- -%} with hyphens to trim whitespace: {% for item in list -%}\n{{ item }}\n{%- endfor %}

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