recommend 503 status code for a service with no healthy endpoints (#3121)

* recommend 503 status code for a service with no healthy endpoints

* MAY=>SHOULD

* Update apis/v1/httproute_types.go

Co-authored-by: Nick Young <[email protected]>

* run codegen

* Update apis/v1/httproute_types.go

Co-authored-by: Nick Young <[email protected]>

* run codegen

---------

Co-authored-by: Nick Young <[email protected]>

Author: dprotaso

apis/v1/httproute_types.go

@@ -263,6 +263,11 @@ type HTTPRouteRule struct {
 	// invalid, 50 percent of traffic must receive a 500. Implementations may
 	// choose how that 50 percent is determined.
 	//
+	// When a HTTPBackendRef refers to a Service that has no ready endpoints,
+	// implementations SHOULD return a 503 for requests to that backend instead.
+	// If an implementation chooses to do this, all of the above rules for 500 responses
+	// MUST also apply for responses that return a 503.
+	//
 	// Support: Core for Kubernetes Service
 	//
 	// Support: Extended for Kubernetes ServiceImport