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05 - Templates

Learn how to render configuration files from templates using pongo2 syntax.

What You'll Learn

  • Rendering .j2 template files
  • Using variables in templates
  • Template conditionals ({% if %})
  • Template loops ({% for %})
  • Passing additional vars to templates

Quick Start

cd examples/05-templates
mooncake run --config config.yml

Check the rendered files: 

ls -lh /tmp/mooncake-templates/
cat /tmp/mooncake-templates/config.yml

What It Does

  1. Defines variables for application, server, and database config
  2. Renders application config with loops and conditionals
  3. Renders nginx config with optional SSL
  4. Creates executable script from template
  5. Renders same template with different variables

Key Concepts

Template Action

- name: Render config
  template:
    src: ./templates/config.yml.j2
    dest: /tmp/config.yml
    mode: "0644"

Template Syntax (pongo2)

Variables: 

{{ variable_name }}
{{ nested.property }}

Conditionals: 

{% if debug %}
  debug: true
{% else %}
  debug: false
{% endif %}

Loops: 

{% for item in items %}
  - {{ item }}
{% endfor %}

Filters: 

{{ path | expanduser }}  # Expands ~ to home directory
{{ text | upper }}       # Convert to uppercase

Passing Additional Vars

Override variables for specific templates: 

- template:
    src: ./templates/config.yml.j2
    dest: /tmp/prod-config.yml
    vars:
      environment: production
      debug: false

Template Files

config.yml.j2

Application configuration with: - Conditional debug settings - Loops over features list - Variable substitution

nginx.conf.j2

Web server config with: - Conditional SSL configuration - Dynamic port and paths

script.sh.j2

Executable shell script with: - Shebang line - Variable expansion - Command loops

Common Use Cases

  • Config files - app.yml, nginx.conf, etc.
  • Shell scripts - deployment scripts, setup scripts
  • Systemd units - service files
  • Dotfiles - .bashrc, .vimrc with customization

Testing Templates

# Render templates
mooncake run --config config.yml

# View rendered output
cat /tmp/mooncake-templates/config.yml

# Check executable permissions
ls -la /tmp/mooncake-templates/deploy.sh

Next Steps

Continue to 06-loops to learn about iterating over lists and files.