Watch Operation should be able to match multiple Kinds

[stevendborrelli]

What problem are you facing?

Currently the watch https://docs.crossplane.io/latest/api/#WatchOperation-spec-watch operation only supports one kind.

Imagine a use case where a platform owner wants to automatically create a Usage object for every resource that has a certain label to prevent accidental deletion, or wants to Watch all the resources in *database.m.crossplane.io apiGroup.

How could Crossplane help solve your problem?

Implement a more flexible match for Watch Operations.

• K8s Webhook rules: https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/#matching-requests-rules
• Kyverno https://release-1-8-0.kyverno.io/docs/writing-policies/match-exclude/

[negz]

Watches are pretty expensive - I think we need to be careful about a controller that could start watching tens or hundreds of types.

For small sets (2, 3, 4 watched kinds) would it be feasible to create a mostly identical WatchOperation per kind? I know its a bit repetitive but I suspect it'll lead to a simpler and easier to reason about system.

[stevendborrelli]

@negz this is a good point. Let's see how watch operations are used in practice.

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