ContainerCluster update failed with googleapi: Error 501: Unimplemented.

[ushuz]

Describe your question

We are using Config Controller and ContainerCluster object to provision a new GKE cluster. The cluster has been successfully created, but ContainerCluster object is stuck in UpdateFailed state with a 501 Unimplemented error:

Status:
  Conditions:
    Last Transition Time:  2025-02-07T15:32:07Z
    Message:               Update call failed: error applying desired state: summary: googleapi: Error 501: Unimplemented.
Details:
[
  {
    "@type": "type.googleapis.com/google.rpc.RequestInfo",
    "requestId": "0x0000ffff"
  },
  {
    "@type": "type.googleapis.com/google.rpc.ErrorInfo",
    "domain": "container.googleapis.com",
    "reason": "UNIMPLEMENTED"
  }
]
, notImplemented
    Reason:             UpdateFailed
    Status:             False
    Type:               Ready

No relevant error logs can be found in container.googleapis.com API's audit logs either.

Question: How to identify what method is failing with 501 Unimplemented?