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Anatomy

Anatomy​

In order to make Starlark work with Vela's templates functionality we did have to make a few design decisions on behalf of the users.

All templates must contain a "main" function that returns the pipeline​

This is illustrated in the below example with a Starlark file that contains a def main(ctx) and returns the data structure that is a valid pipeline.

def main(ctx):
  return {
    'version': '1',
    'steps': [
      {
        'name': 'build',
        'image': 'golang:latest',
        'commands': [
          'go build',
          'go test',
        ]
      },
    ],
}

Context is used by the compiler to pass information to the template​

The compiler will inject user variables defined in the parent template and compile time platform variables. Both sets of variables are injected into the context within a dictionary structure.

Platform variables​

Syntax: ctx['vela']['<resource>']['<name>']

def main(ctx):
  repo = ctx["vela"]["repo"]["full_name"]

  return {
    'version': '1',
    'steps': [
      {
        'name': 'build',
        'image': 'golang:latest',
        'commands': [
          "go build %s" %, repo,
          'go test',
        ]
      },
    ],
}

Template variables​

Syntax: ctx['vars'][<name>]

def main(ctx):
  image = ctx['vars']['image']

  return {
    'version': '1',
    'steps': [
      {
        'name': 'build',
        'image': image,
        'commands': [
          'go build',
          'go test',
        ]
      },
    ],
}