Support informer names in the kcp cluster informer factory #4518

Context

While preparing the Kubernetes 1.37 patches (kcp-dev/kubernetes-patches#2), upstream's BuildGenericConfig in pkg/controlplane/apiserver/config.go now builds the shared informer factory with clientgoinformers.WithInformerName(informerName), which gives the informers an identity for informer metrics.

The kcp carry (patches/0025-UPSTREAM-carry-generic-cleanup.patch) replaces that factory with the kcp cluster-aware one, kcpinformers.NewSharedInformerFactoryWithOptions(clusterClient, ...). That factory has no equivalent option, so the carry drops the call and leaves a comment:

Upstream additionally sets WithInformerName(informerName) for informer identity metrics; the kcp cluster informer factory does not support informer names (yet), so the identifier is unused here.

Result: informers created through the kcp factory in the generic apiserver config have no name, so they are missing from upstream's informer-identity metrics, and the carry diverges from upstream here.

What to do

Look into supporting informer names in the kcp cluster informer factory and the cluster-aware informers it creates, so the kcp patch can pass WithInformerName(informerName) again. This likely needs a change in the kcp-dev client-go / code-generator output, not only in this repo.

• Find where the kcp cluster informer factory (kcpinformers) is generated, and which client-go informer API accepts an informer name
• Add a WithInformerName option to the factory options and pass the name through to the underlying informers (scoped and cluster-wide)
• Regenerate the informers and bump the dependency in kcp
• Restore kcpinformers.WithInformerName(informerName) in the BuildGenericConfig carry patch and delete the explanatory comment
• If this is not feasible, record that decision so the divergence from upstream is intentional

References

• PR: patches for 1.37 kubernetes-patches#2
• Requesting comment: patches for 1.37 kubernetes-patches#2 (comment)