Question: Why use labels and not annotations?

[twobiers]

I just stumbled across this function and believe it would be a good fit in our environment. However, while taking a closer look I was wondering why function relies on labels but not annotations. Also #7 includes a new label.
For example function-go-templating supports setting an gotemplating.fn.crossplane.io/composition-resource-name annotation to be used together with the function.

Am I missing any internal of crossplane that requires using labels here?

From the Kubernetes Documentation:

Labels	Annotations
Labels are key/value pairs that are attached to objects such as Pods. Labels are intended to be used to specify identifying attributes of objects that are meaningful and relevant to users, but do not directly imply semantics to the core system.	You can use Kubernetes annotations to attach arbitrary non-identifying metadata to objects. Clients such as tools and libraries can retrieve this metadata.

[stevendborrelli]

Hello @twobiers I will look into this, but the convention in Crossplane has been to use labels to select resources. But there is a good argument to align with other k8s tools and use annotations instead.

• Watch Operations https://docs.crossplane.io/latest/operations/watchoperation/#watch-resources-with-specific-labels
• Composition selectors: https://docs.crossplane.io/latest/composition/composition-revisions/#using-a-selector
• EnvironmentConfigs https://docs.crossplane.io/latest/composition/environment-configs/#select-an-environmentconfig-using-function-environment-configs
• Resource Selectors in MRs, like https://marketplace.upbound.io/providers/upbound/provider-aws-ec2/v2.3.0/resources/ec2.aws.m.upbound.io/Subnet/v1beta1#doc:spec-forProvider-vpcIdSelector-matchLabels

[stevendborrelli]

@twobiers after some research, I agree with you on using annotations instead. If you want to submit any PR to support annotations, I'll be happy to approve and merge them. Otherwise, I will migrate to annotations as we add features.