function-sequencer

Function Sequencer is a Crossplane function that enables Composition authors to define sequencing rules delaying the creation of resources until other resources are ready.

For example, the pipeline step below, will ensure that second-resource and third-resource not to be created until the first-resource is ready.

  - step: sequence-creation
    functionRef:
      name: function-sequencer
    input:
      apiVersion: sequencer.fn.crossplane.io/v1beta1
      kind: Input
      rules:
        - sequence:
          - first-resource
          - second-resource
        - sequence:
          - first-resource
          - third-resource

See example/composition.yaml for a complete example.

It also allows you to provide a regex to match and capture a whole group of resources and wait for them to be ready.

For example, the pipeline step below, will ensure that second-resource is not created until all first-subresource-.* objects are ready.

  - step: sequence-creation
    functionRef:
      name: function-sequencer
    input:
      apiVersion: sequencer.fn.crossplane.io/v1beta1
      kind: Input
      rules:
        - sequence:
          - first-subresource-.*
          - second-resource

You can write the regex as strict as you want, but keep in mind that it defaults to strict matching (start and end are enforced). In other words, the following rules apply:

- resource    # this has no explicit start or end, so it will match EXACTLY ^resource$ (normal behaviour)
- a-group-.*  # this has no explicit start or end, so it will match EXACTLY ^a-group-.*$
- ^a-group    # this has an explicit start, so it will match EVERYTHING that starts with a-group
- a-group$    # this has an explicit end, so it will match EVERYTHING that ends with a-group

See example/composition-regex.yaml for a complete example.

Composite Readiness

Enabling the resetCompositeReadiness flag causes the function to set the Composite's Ready flag to False when at least one desired resource is deleted from the request. This prevents the Composite resource from entering the Ready state prematurely when there are pending resources that the composite reconciler is unaware of.

  - step: sequence-creation
    functionRef:
      name: function-sequencer
    input:
      apiVersion: sequencer.fn.crossplane.io/v1beta1
      kind: Input
      resetCompositeReadiness: true
      rules:
        - sequence:
          - first-subresource-.*
          - second-resource

Installation

It can be installed as follows from the Upbound marketplace: https://marketplace.upbound.io/functions/crossplane-contrib/function-sequencer

Developing this function

You can use go run to run your function locally

go run . --insecure --debug

After that, you can use Crossplane CLI's crossplane render to test what your function is doing.

To test a sequence:

# --observed-resources allows you to simulate already created objects
crossplane render example/xr.yaml example/composition.yaml example/functions.yaml --observed-resources example/observed.yaml

To test a regex sequence:

# --observed-resources allows you to simulate already created objects
crossplane render example/xr.yaml example/composition-regex.yaml example/functions.yaml --observed-resources example/observed-regex.yaml