Ansible Essentials: Jinja2 Templates

Hardcoding values in config files works for one host — but when you manage ten servers with slightly different settings, you end up maintaining ten nearly identical files. Jinja2 templates let you write a single file with placeholders that Ansible fills in per host at deploy time.

Template Syntax

Templates are plain text files ending in .j2 with three main expressions:

Where Templates Live

Place templates inside your role under a templates/ directory:

roles/
└── monitoring/
    ├── tasks/
    │   └── main.yml
    └── templates/
        └── prometheus-targets.j2

The template Module

Use template instead of copy whenever you need variable substitution:

- name: Deploy Prometheus scrape config
  ansible.builtin.template:
    src: prometheus-targets.j2
    dest: /etc/prometheus/targets.yml
    owner: prometheus
    group: prometheus
    mode: '0644'
  notify: Reload Prometheus

Writing a Template

This template generates a Prometheus scrape config from your inventory:

# Managed by Ansible — do not edit manually
scrape_configs:
  - job_name: node_exporter
    static_configs:
      - targets:
{%- for host in groups['homelab'] %}
          - "{{ hostvars[host]['ansible_host'] }}:9100"
{%- endfor %}

Add a host to your inventory and the next run updates the config automatically.

Use {% if %} to include sections conditionally:

{% if enable_https %}
    scheme: https
    tls_config:
      insecure_skip_verify: true
{% endif %}

Directory Structure

homelab-ansible/
├── inventory/
│   └── hosts.yml
├── group_vars/
│   └── all.yml
├── playbooks/
│   └── monitoring.yml
└── roles/
    └── monitoring/
        ├── tasks/
        │   └── main.yml
        └── templates/
            └── prometheus-targets.j2

Create the Playbook

- name: Deploy monitoring config
  hosts: monitoring_server
  become: true
  roles:
    - monitoring

Run It

ansible-playbook playbooks/monitoring.yml --ask-become-pass

Recap

You’ve learned how to:

• Write .j2 templates using {{ }}, {% if %}, and {% for %} syntax
• Place templates inside a role’s templates/ directory
• Deploy rendered files with the template module

Next up: Variables & Facts — how Ansible collects information about your hosts.