Indirect Length Limitation of EventRecorder Name

[brito-rafa]

The migration to controller-runtime 0.23.1 introduced stricter validation
for event recorder names using the events.k8s.io API group.

The new API enforces that reportingController names must be valid Kubernetes qualified
names matching the regex: ([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9].

So far was good, but it seems that once the event is created, the event field
reportingInstance is populated from reportingController+reconciliationId.
And the reportingInstance has a limitation of 128 chars and hence we now have a limitation of
reportingController.
As per events doc:

reportingController (string)
reportingController is the name of the controller that emitted this Event, e.g. kubernetes.io/kubelet. This field cannot be empty for new Events.
reportingInstance (string)
reportingInstance is the ID of the controller instance, e.g. kubelet-xyzf. This field cannot be empty for new Events and it can have at most 128 characters.

Here our error log message :

E0501 20:33:03.500254       1 event_broadcaster.go:270] "Server rejected event (will not retry!)" err="Event \"windows-laav-a2.18ab8b3faaa83129\" is invalid: reportingInstance: Invalid value: \"\": can have at most 128 characters" event="&Event{ObjectMeta:{windows-laav-a2.18ab8b3faaa83129  vmsvc-e2e-so7rzi    0 0001-01-01 00:00:00 +0000 UTC <nil> <nil> map[] map[] [] [] []},EventTime:2026-05-01 20:33:03.490136698 +0000 UTC m=+27.204947134,Series:nil,ReportingController:vmware-system-vmop.vmware-system-vmop-controller-manager-7f885ffff5-mlnhc/virtualmachine-controller,ReportingInstance:vmware-system-vmop.vmware-system-vmop-controller-manager-7f885ffff5-mlnhc/virtualmachine-controller-423b393286e26d68e9777202c42da01a,Action:UpdateSuccess,Reason:UpdateSuccess,Regarding:{VirtualMachine vmsvc-e2e-so7rzi windows-laav-a2 a228f522-3a3b-43e9-8b5e-36eaa1b92e12 vmoperator.vmware.com/v1alpha6 5978637 },Related:nil,Note:Update success,Type:Normal,DeprecatedSource:{ },DeprecatedFirstTimestamp:0001-01-01 00:00:00 +0000 UTC,DeprecatedLastTimestamp:0001-01-01 00:00:00 +0000 UTC,DeprecatedCount:0,}"

[brito-rafa]

Let me put more colour on the Event object generated. I think I took a leap of faith flagging the suffix as a Reconcile ID, perhaps it is not. Please see below the difference between the two fields, reportingController and reportingInstance. The difference it is the suffix, which has length of 32 char.

{
  "kind": "Event",
  "apiVersion": "events.k8s.io/v1",
  "metadata": {
    "name": "common-photon-vm-tecb.18ab8408dbf84c92",
    "namespace": "common-photon-vm-tecb",
    "creationTimestamp": "0001-01-01T00:00:00Z"
  },
  "regarding": {
    "kind": "VirtualMachine",
    "namespace": "common-photon-vm-tecb",
    "name": "vmsvc-e2e-so7rzi",
    "uid": "fa623a95-b62b-45f9-8545-586b15fe61af",
    "apiVersion": "vmoperator.vmware.com/v1alpha6",
    "resourceVersion": "5892264"
  },
  "eventTime": "2026-05-01T18:20:51.512875Z",
  "series": {
    "count": 2,
    "lastObservedTime": "2026-05-01T18:23:45.549337Z"
  },
  "reportingController": "vmware-system-vmop.vmware-system-vmop-controller-manager-d8bcb8f8b-9dmgd/virtualmachine-controller",
  "reportingInstance": "vmware-system-vmop.vmware-system-vmop-controller-manager-d8bcb8f8b-9dmgd/virtualmachine-controller-423b393286e26d68e9777202c42da01a",
  "action": "UpdateSuccess",
  "reason": "UpdateSuccess",
  "note": "Update success",
  "type": "Normal",
  "deprecatedSource": {},
  "deprecatedFirstTimestamp": "0001-01-01T00:00:00Z",
  "deprecatedLastTimestamp": "0001-01-01T00:00:00Z",
  "deprecatedCount": 0
}

[sbueringer]

I think there's not much we can do in controller-runtime beyond documenting this constraint on the mgr.GetEventRecorder method.

The event is generated here in client-go: https://github.com/kubernetes/client-go/blob/master/tools/events/event_recorder.go#L84

Based on data computed here: https://github.com/kubernetes/client-go/blob/master/tools/events/event_broadcaster.go#L165-L167

(reportingInstance is the name passed into GetEventRecorder with the hostname as a suffix. Usually the hostname is equal to the Pod name of the controller)