Template Helpers

Lono provides a few built-in helper methods that help with template processing. These methods are available in your template views - the files in the templates folder. Here’s a list of the common helper methods:

Helper Description
extract_scripts Generates a script that can be included in user_data scripts to extract app/script files. More info about the helper is in the App Scripts docs.
s3_key(name) Helper method that references the s3 key of the file uploaded in app/files.
indent(text, amount) This is a helper method indents the provided string by a specified number of spaces.
partial(name, variables, options) Can be used to embed other files in a template. The partial view should be placed in the templates/partial folder of the project.
partial_exist?(name) Checks whether a partial name exists. This can be helpful for writing custom helpers, covered in Custom Helpers
template_params(name) This returns an Array of the parameter values. This is useful in a parent template if you are using nested templates. You can use this to grab the params values and specify the parameters within the parent template.
template_s3_path(name) This is the s3 path where template gets uploaded to s3.
user_data(path, vars, options) Helper method includes files in the app/user_data folder.

The full list of helper methods is available here: lib/lono/template/helper.rb.

Partial examples

The partial template helper is useful and is covered a little more detail here:

  • partial('launch_config') - Uses the partial in templates/partial/launch_config.
  • partial('launch_config', foo: "bar", hello: "world") - Variables can be passed to the partial helper method are available to the partial as instance variables. So, in this case @foo and @hello will be available in the launch_config partial.
  • partial('user_data/bootstrap.sh', {}, indent: 10) - Indent the result partial by 10 spaces. Useful for yaml format.

Next, we’ll cover how you add custom helpers.

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