state: handle terminating gateways in service health events

agent/consul/state/catalog_events.go

@@ -218,17 +218,8 @@ func ServiceHealthEventsFromChanges(tx ReadTxn, changes Changes) ([]stream.Event
 				events = append(events, e)
 			}
 
-			if before.ServiceKind == structs.ServiceKindConnectProxy &&
-				before.ServiceProxy.DestinationServiceName != after.ServiceProxy.DestinationServiceName {
-				// Connect proxy changed the service it is representing, need to issue a
-				// dereg for the old service on the Connect topic. We don't actually need
-				// to deregister this sidecar service though as it still exists and
-				// didn't change its name (or if it did that was caught just above). But
-				// our mechanism for connect events is to convert them so we generate
-				// the regular one, convert it to Connect topic and then discard the
-				// original.
-				e := newServiceHealthEventDeregister(changes.Index, before)
-				events = append(events, serviceHealthToConnectEvents(e)...)
+			if e, ok := isConnectProxyDestinationServiceChange(changes.Index, before, after); ok {
+				events = append(events, e)
 			}
 		}
 
@@ -252,6 +243,22 @@ func ServiceHealthEventsFromChanges(tx ReadTxn, changes Changes) ([]stream.Event
 	return events, nil
 }
 
+// isConnectProxyDestinationServiceChange handles the case where a Connect proxy changed
+// the service it is proxying. We need to issue a de-registration for the old
+// service on the Connect topic. We don't actually need to deregister this sidecar
+// service though as it still exists and didn't change its name.
+func isConnectProxyDestinationServiceChange(idx uint64, before, after *structs.ServiceNode) (stream.Event, bool) {
+	if before.ServiceKind != structs.ServiceKindConnectProxy ||
+		before.ServiceProxy.DestinationServiceName == after.ServiceProxy.DestinationServiceName {
+		return stream.Event{}, false
+	}
+
+	e := newServiceHealthEventDeregister(idx, before)
+	e.Topic = TopicServiceHealthConnect
+	e.Key = getPayloadCheckServiceNode(e.Payload).Service.Proxy.DestinationServiceName
+	return e, true
+}
+
 type changeType uint8
 
 const (
@@ -281,33 +288,35 @@ func changeTypeFromChange(change memdb.Change) changeType {
 // switching connection details to be the proxy instead of the actual instance
 // in case of a sidecar.
 func serviceHealthToConnectEvents(events ...stream.Event) []stream.Event {
-	var serviceHealthConnectEvents []stream.Event
+	var result []stream.Event
 	for _, event := range events {
 		if event.Topic != TopicServiceHealth {
 			// Skip non-health or any events already emitted to Connect topic
 			continue
 		}
 		node := getPayloadCheckServiceNode(event.Payload)
-		// TODO: do we need to handle gateways here as well?
-		if node.Service == nil ||
-			(node.Service.Kind != structs.ServiceKindConnectProxy && !node.Service.Connect.Native) {
-			// Event is not a service instance (i.e. just a node registration)
-			// or is not a service that is not connect-enabled in some way.
+		if node.Service == nil {
 			continue
 		}
 
 		connectEvent := event
 		connectEvent.Topic = TopicServiceHealthConnect
 
-		// If this is a proxy, set the key to the destination service name.
-		if node.Service.Kind == structs.ServiceKindConnectProxy {
-			connectEvent.Key = node.Service.Proxy.DestinationServiceName
-		}
+		switch {
+		case node.Service.Connect.Native:
+			result = append(result, connectEvent)
 
-		serviceHealthConnectEvents = append(serviceHealthConnectEvents, connectEvent)
+		case node.Service.Kind == structs.ServiceKindConnectProxy:
+			connectEvent.Key = node.Service.Proxy.DestinationServiceName
+			result = append(result, connectEvent)
+
+		default:
+			// ServiceKindTerminatingGateway changes are handled separately.
+			// All other cases are not relevant to the connect topic
+		}
 	}
 
-	return serviceHealthConnectEvents
+	return result
 }
 
 func getPayloadCheckServiceNode(payload interface{}) *structs.CheckServiceNode {