Lab 011 - `Jinja2` Templating¶

During our day to day job, we come across dozens of configuration files, set in many different formats.
What happens if we need to configure different environments, each with its own values? Should we duplicate the same file for each one?
This is where Jinja2 templates come to the rescue! Jinja2 helps us template our configuration files to be used with different values and reduce duplications.
Jinja2 is a powerful templating engine integrated into Ansible, used commonly in python projects.
Templates allow dynamic configuration file generation, based on variables and facts.
Jinja2 can be used with conditionals and loops and can even perform filters and functions on our values!

01. Creating Jinja2 templates¶

Create a Jinja2 template file by appending a .j2 suffix to our base config filename. For example, nginx.conf.j2:

# Example

events {}
http {
  server {
    listen {{ web_port }};
    server_name {{ domain_name }};

    location / {
      proxy_pass http://{{ backend_ip }}:{{ backend_port }};
    }
  }
}

02. Using templates in playbooks¶

Integrate Jinja2 templates using the ansible.builtin.template module:

---
- hosts: web_servers
  vars:
    web_port: 80
    domain_name: example.com
    backend_ip: 192.168.10.10
    backend_port: 8080
  tasks:
    - name: Deploy Nginx Configuration
      ansible.builtin.template:
        src: config.j2
        dest: /etc/nginx/conf.d/site.conf
      notify: Restart Nginx

  handlers:
    - name: Restart Nginx
      ansible.builtin.service:
        name: nginx
        state: restarted

03. Using conditional statements¶

jinja2 supports conditional logic to dynamically alter configurations:

{% if ansible_distribution == 'Ubuntu' %}
User ubuntu;
{% elif ansible_distribution == 'CentOS' %}
User centos;
{% else %}
User default;
{% endif %}

04. Looping with `Jinja2`¶

Jinja2 makes it easy to iterate over lists or dictionaries:

# hosts file
{% for host in groups['web_servers'] %}
{{ hostvars[host]['ansible_default_ipv4']['address'] }} {{ host }}
{% endfor %}

05. Filters and functions¶

Jinja2 includes built-in filters to transform data:

# Convert text to uppercase
ServerName {{ domain_name | upper }}

# Default filter for fallback values
Listen {{ custom_port | default(8080) }}

06. Summary¶

🔹 Jinja2 enables dynamic template generation with variables and facts.
🔹 Templates help manage complex configurations in a more simple and efficient manner.
🔹 Use conditional statements and loops for highly dynamic setups.
🔹 Built-in filters enhance the manipulation of data directly within templates.

Practice

07. Hands-on¶

Create a Jinja2 template for generating a dynamic /etc/motd (“Message of the Day”) file, containing a personal message (ensure first that it is enabled).
The relevant code can be found in lab 009.
Bonus: Use facts to display useful information about OS distribution, IP address and current hostname dynamically when logging in.

Lab 011 - Jinja2 Templating¶