Functions require inputs and outputs to process requests and return values to your control plane.

Inputs

Compositions execute in a pipeline of one or more sequential functions. A function updates desired resource state and returns it to Crossplane. Function requests and values rely on three pieces of information:

1. The observed state of the composite resource, and any composed resources.
2. The desired state of the composite resource, and any composed resources.
3. The function pipeline’s context.

Each composition pipeline provides this information as inputs into the function.

Function inputs are available to Go templates in the following template inputs, which templates can access directly or with helper functions:

• Observed state: .observed
  • The getCompositeResource helper function fetches the observed composite resource.
  • The getComposedResource helper function looks up an observed composed resource.
• Desired state: .desired
• Pipeline context: .context

Outputs

To add resources to the pipeline’s desired composed resources, define them in the template. Use the gotemplating.fn.crossplane.io/composition-resource-name annotation to define unique names for each resource. This allows you to update a resource rather than create a new one on subsequent functions runs. The setResourceNameAnnotation helper function sets this annotation:

# code: language=yaml
# yaml-language-server: $schema=../../.up/json/models/index.schema.json

---
apiVersion: s3.aws.upbound.io/v1beta1
kind: Bucket
metadata:
  annotations:
    {{ setResourceNameAnnotation "bucket" }}
spec:
  forProvider:
    region: "{{ $xr.spec.parameters.region }}"

To update the composite resource’s status, have your templates output a resource of the composite’s type without the composition-resource-name annotation:

# code: language=yaml
# yaml-language-server: $schema=../../.up/json/models/index.schema.json

---
apiVersion: devexdemo.upbound.io/v1alpha1
kind: XBucket
status:
  someInformation: cool-status

To set conditions on the claim and composite, you can add a ClaimConditions resource to your templates:

apiVersion: meta.gotemplating.fn.crossplane.io/v1alpha1
kind: ClaimConditions
conditions:
- type: BucketReady
  status: "True"
  reason: Ready
  message: Bucket is ready
  target: CompositeAndClaim