Validation to ensure that the CRD exists – Handling the non-existent CRD scenario.

[rahtr]

Describe the bug
When the CRD doesn't exist, the controller errors out. This behavior is expected from the application. However, from a platform's perspective, there are scenarios where CRDs are enabled by platform operators, and controllers are deployed by ACK controller admins. Though an edge case, there could be instances where the CRDs enabled by platform operators lag behind the controller version, or scenarios where platform operators only want to enable certain versions on the platform. In this situation, the controller would remain in an error state since it wouldn't find the required CRD.

For example, consider the ElastiCache release version v0.0.29, which didn't have the CacheCluster CR, only added in version v0.1.0.

{"level":"error","ts":"2024-08-21T13:57:27.722Z","logger":"controller-runtime.source.EventHandler","msg":"if kind is a CRD, it should be installed before calling Start","kind":"CacheCluster.elasticache.services.k8s.aws","error":"no matches for kind \"CacheCluster\" in version \"elasticache.services.k8s.aws/v1alpha1\"","stacktrace":"sigs.k8s.io/controller-runtime/pkg/internal/source.(*Kind).Start.func1.1\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.2/pkg/internal/source/kind.go:63\nk8s.io/apimachinery/pkg/util/wait.loopConditionUntilContext.func2\n\t/go/pkg/mod/k8s.io/apimachinery@v0.29.0/pkg/util/wait/loop.go:87\nk8s.io/apimachinery/pkg/util/wait.loopConditionUntilContext\n\t/go/pkg/mod/k8s.io/apimachinery@v0.29.0/pkg/util/wait/loop.go:88\nk8s.io/apimachinery/pkg/util/wait.PollUntilContextCancel\n\t/go/pkg/mod/k8s.io/apimachinery@v0.29.0/pkg/util/wait/poll.go:33\nsigs.k8s.io/controller-runtime/pkg/internal/source.(*Kind).Start.func1\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.2/pkg/internal/source/kind.go:56"}

Steps to reproduce

Expected outcome
Is there a possibility to add an ignore CRD check in the runtime?

Environment

• Kubernetes version 1.28
• Using EKS (yes/no), if so version? yes
• AWS service targeted (S3, RDS, etc.): We observed this on the Elasticache controller but it's valid for other controllers as well.

[gecube]

Hi!

What is the difference with #2007 ? So this ticket is enhancing that one.

Is there a possibility to add an ignore CRD check in the runtime?

It means that then we need to disable handling of particular crds in controller... otherwise it will silently ignore some crds and the operator of cluster won't know that some functions are not ... let's say enabled.

Also I want to say that from my perspective it would be a very rare case when somebody (not platform operator!) should install ACK toolkit. It looks like that only platform operators should install the ACK operators in the cluster and follow strict procedure (CRDs before, the operator itself after).