Templates Operator

The Templates operator renders a remote or inline template to a local file, injecting environment variables and optional per-step variables.

Syntax 

- template: <LOCAL_DESTINATION_PATH>
  source: <REMOTE_LOCATION_OR_URL>
  vars:
    - type: <value|command>
      input: <INPUT>
      variable: <VARIABLE_NAME>
  onlyIf: <sub-command>
  notIf: <sub-command>
  exitIf: <sub-command>
  • template: Local destination path written by this operator.
  • source: Remote template source. Supports file://, http(s)://, and s3:// URLs.
  • vars: Optional list of variables to add/override when rendering the template.
  • type:
    • value: Use the literal input value (supports OS handler mapping; see below).
    • command: Execute input as a command and use its stdout.
  • input: The value or command to evaluate for the variable.
  • variable: The variable name made available to the template (merged on top of existing environment variables).
  • onlyIf: See detailed docs here
  • notIf: See detailed docs here
  • exitIf: See detailed docs here

Note: Fields perms, owner, and group exist in the configuration model but are not currently applied by the implementation. Files are created with default mode 0664, and ownership is unchanged.

Example: 

- template: /etc/nginx/nginx.conf
  source: https://raw.githubusercontent.com/brucedom/bruce/main/examples/nginx/templates/etc/nginx/nginx.conf
  vars:
  - type: value
    input: nginx|apt=www-data
    variable: NGINX_USER

In this example, the Templates operator downloads the Nginx configuration file from the provided URL and saves it to /etc/nginx/nginx.conf. It injects the variable NGINX_USER using OS handler mapping: nginx|apt=www-data means use nginx by default, but if the package handler is apt, use www-data. See GetValueForOSHandler() in bruce/operators/operators.go.

Example 2: 

- template: /etc/nginx/nginx.conf
  source: https://raw.githubusercontent.com/brucedom/bruce/main/examples/nginx/templates/etc/nginx/nginx.conf
  vars:
  - type: value
    input: nginx|apt=www-data
    variable: NGINX_USER
  notIf: ls /etc/systemd/system/nginx.service

In the above example, the Templates operator only executes if the /etc/systemd/system/nginx.service file does not exist.

Example 3: 

- template: /etc/nginx/nginx.conf
  source: https://raw.githubusercontent.com/brucedom/bruce/main/examples/nginx/templates/etc/nginx/nginx.conf
  vars:
  - type: value
    input: nginx|apt=www-data
    variable: NGINX_USER
  onlyIf: ls /tmp/output.txt

In the above example, the Templates operator only executes if the /tmp/output.txt file exists.

Variable sources and Templating

  • Environment variables are always injected into the template render context.
  • vars entries override or add to those values.
  • Two custom template functions are available:
    • contains substr value: returns true if value contains substr.
    • dump .: pretty-prints a value for debugging.

Example 4: Using a command-based variable 

- template: /etc/example.conf
  source: https://example.com/templates/example.conf.tmpl
  vars:
    - type: command
      input: hostname -f
      variable: HOST_FQDN

The HOST_FQDN variable will contain the output of hostname -f.