Merge pull request #74959 from deads2k/hook-reg

staging/src/k8s.io/apiserver/pkg/server/hooks.go

@@ -20,6 +20,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"runtime/debug"
 
 	"k8s.io/klog"
 
@@ -58,6 +59,9 @@ type PostStartHookProvider interface {
 
 type postStartHookEntry struct {
 	hook PostStartHookFunc
+	// originatingStack holds the stack that registered postStartHooks. This allows us to show a more helpful message
+	// for duplicate registration.
+	originatingStack string
 
 	// done will be closed when the postHook is finished
 	done chan struct{}
@@ -85,8 +89,9 @@ func (s *GenericAPIServer) AddPostStartHook(name string, hook PostStartHookFunc)
 	if s.postStartHooksCalled {
 		return fmt.Errorf("unable to add %q because PostStartHooks have already been called", name)
 	}
-	if _, exists := s.postStartHooks[name]; exists {
-		return fmt.Errorf("unable to add %q because it is already registered", name)
+	if postStartHook, exists := s.postStartHooks[name]; exists {
+		// this is programmer error, but it can be hard to debug
+		return fmt.Errorf("unable to add %q because it was already registered by: %s", name, postStartHook.originatingStack)
 	}
 
 	// done is closed when the poststarthook is finished.  This is used by the health check to be able to indicate
@@ -95,7 +100,7 @@ func (s *GenericAPIServer) AddPostStartHook(name string, hook PostStartHookFunc)
 	if err := s.AddHealthzChecks(postStartHookHealthz{name: "poststarthook/" + name, done: done}); err != nil {
 		return err
 	}
-	s.postStartHooks[name] = postStartHookEntry{hook: hook, done: done}
+	s.postStartHooks[name] = postStartHookEntry{hook: hook, originatingStack: string(debug.Stack()), done: done}
 
 	return nil
 }