[core] changes to distribution of kafka messages to partitions

- added environment id as a key to messages containing environment id
field
- changed Balancer from LeastBytes to Hash which makes kafka-go puts
messages with same key to the same partition, fixing ordering problems

Author: Michal Tichák

common/event/writer.go

@@ -62,7 +62,7 @@ func NewWriterWithTopic(topic topic.Topic) *KafkaWriter {
 		Writer: &kafka.Writer{
 			Addr:                   kafka.TCP(viper.GetStringSlice("kafkaEndpoints")...),
 			Topic:                  string(topic),
-			Balancer:               &kafka.LeastBytes{},
+			Balancer:               &kafka.Hash{},
 			AllowAutoTopicCreation: true,
 		},
 	}
@@ -80,6 +80,18 @@ func (w *KafkaWriter) WriteEvent(e interface{}) {
 	}
 }
 
+type HasEnvID interface {
+	GetEnvironmentId() string
+}
+
+func extractAndConvertEnvID[T HasEnvID](object T) []byte {
+	envID := []byte(object.GetEnvironmentId())
+	if len(envID) > 0 {
+		return envID
+	}
+	return nil
+}
+
 func (w *KafkaWriter) WriteEventWithTimestamp(e interface{}, timestamp time.Time) {
 	if w == nil {
 		return
@@ -89,6 +101,7 @@ func (w *KafkaWriter) WriteEventWithTimestamp(e interface{}, timestamp time.Time
 		var (
 			err          error
 			wrappedEvent *pb.Event
+			key          []byte = nil
 		)
 
 		switch e := e.(type) {
@@ -111,36 +124,42 @@ func (w *KafkaWriter) WriteEventWithTimestamp(e interface{}, timestamp time.Time
 				Payload:       &pb.Event_FrameworkEvent{FrameworkEvent: e},
 			}
 		case *pb.Ev_TaskEvent:
+			key = extractAndConvertEnvID(e)
 			wrappedEvent = &pb.Event{
 				Timestamp:     timestamp.UnixMilli(),
 				TimestampNano: timestamp.UnixNano(),
 				Payload:       &pb.Event_TaskEvent{TaskEvent: e},
 			}
 		case *pb.Ev_RoleEvent:
+			key = extractAndConvertEnvID(e)
 			wrappedEvent = &pb.Event{
 				Timestamp:     timestamp.UnixMilli(),
 				TimestampNano: timestamp.UnixNano(),
 				Payload:       &pb.Event_RoleEvent{RoleEvent: e},
 			}
 		case *pb.Ev_EnvironmentEvent:
+			key = extractAndConvertEnvID(e)
 			wrappedEvent = &pb.Event{
 				Timestamp:     timestamp.UnixMilli(),
 				TimestampNano: timestamp.UnixNano(),
 				Payload:       &pb.Event_EnvironmentEvent{EnvironmentEvent: e},
 			}
 		case *pb.Ev_CallEvent:
+			key = extractAndConvertEnvID(e)
 			wrappedEvent = &pb.Event{
 				Timestamp:     timestamp.UnixMilli(),
 				TimestampNano: timestamp.UnixNano(),
 				Payload:       &pb.Event_CallEvent{CallEvent: e},
 			}
 		case *pb.Ev_IntegratedServiceEvent:
+			key = extractAndConvertEnvID(e)
 			wrappedEvent = &pb.Event{
 				Timestamp:     timestamp.UnixMilli(),
 				TimestampNano: timestamp.UnixNano(),
 				Payload:       &pb.Event_IntegratedServiceEvent{IntegratedServiceEvent: e},
 			}
 		case *pb.Ev_RunEvent:
+			key = extractAndConvertEnvID(e)
 			wrappedEvent = &pb.Event{
 				Timestamp:     timestamp.UnixMilli(),
 				TimestampNano: timestamp.UnixNano(),
@@ -151,7 +170,7 @@ func (w *KafkaWriter) WriteEventWithTimestamp(e interface{}, timestamp time.Time
 		if wrappedEvent == nil {
 			err = fmt.Errorf("unsupported event type")
 		} else {
-			err = w.doWriteEvent(wrappedEvent)
+			err = w.doWriteEvent(key, wrappedEvent)
 		}
 
 		if err != nil {
@@ -162,7 +181,7 @@ func (w *KafkaWriter) WriteEventWithTimestamp(e interface{}, timestamp time.Time
 	}()
 }
 
-func (w *KafkaWriter) doWriteEvent(e *pb.Event) error {
+func (w *KafkaWriter) doWriteEvent(key []byte, e *pb.Event) error {
 	if w == nil {
 		return nil
 	}
@@ -172,10 +191,15 @@ func (w *KafkaWriter) doWriteEvent(e *pb.Event) error {
 		return fmt.Errorf("failed to marshal event: %w", err)
 	}
 
-	err = w.WriteMessages(context.Background(), kafka.Message{
+	message := kafka.Message{
 		Value: data,
-	})
+	}
+
+	if key != nil {
+		message.Key = key
+	}
 
+	err = w.WriteMessages(context.Background(), message)
 	if err != nil {
 		return fmt.Errorf("failed to write event: %w", err)
 	}