I'm trying to find the issue where this option was discussed and discarded several releases ago, @thockin @robscott do you remember?

This fixes the issue because it process its own update, we are already doing it on other controllers, but it means we are going to do double the work now for each endpoint update

I found this change would break a conformance test: "should test the lifecycle of an Endpoint".
However, the conformance test itself seems contradictory with some logic of endpoints controller:

• The conformance test expects an Endpoint created without a Service to exist
• The checkLeftoverEndpoints function of endpoint controller triggers syncing all Endpoints except for those having leader election annotation and will cause Endpoints without Services to be deleted:

  kubernetes/pkg/controller/endpoint/endpoints_controller.go

  Lines 561 to 567 in 921fb0b

  	// checkLeftoverEndpoints lists all currently existing endpoints and adds their
  	// service to the queue. This will detect endpoints that exist with no
  	// corresponding service; these endpoints need to be deleted. We only need to
  	// do this once on startup, because in steady-state these are detected (but
  	// some stragglers could have been left behind if the endpoint controller
  	// reboots).
  	func (e *Controller) checkLeftoverEndpoints() {

The conformance test gives an impression that an user created Endpoints (without a Service) can exist but it will be deleted once kube-controller-manager restarts or fails over. Subscribing endpoints update events extends the cleanup logic of checkLeftoverEndpoints in a sense.

It seems the conformance test would fail as long as the controller watches endpoints update events.

I'm thinking another fix which doesn't affect the conformance test and could avoid doubling the work: we track the stale resource versions of endpoints after each successful endpoints update, use it to determine whether the endpoints in cache is stale when syncing it next time, and return error if it's stale and retry. (The reason why we don't track generation like endpointslice controller is endpoints doesn't have a generation.)

The 2nd commit implements the above fix.

I'm trying to find the issue where this option was discussed and discarded several releases ago, @thockin @robscott do you remember?

I definitely remember what you're talking about, but not the details...