Apache Camel Kafka - aggregate kafka messages and publish to a different topic at regular intervals

Question

I have a usecase:

I need to read and aggregate messages from a kafka topic at regular intervals and publish to a different topic. Localstorage is not an option. This is how I am planning to address this, any suggestions to improve are welcome

To schedule the aggregation and publishing of kafka messages, planning to use completionInterval option of Aggregator EIP. Here is the code.

  @Autowired ObjectMapper objectMapper;
  JacksonDataFormat jacksonDataFormat;

  @PostConstruct
  public void initialize(){
    //objectMapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
    jacksonDataFormat = new JacksonDataFormat(objectMapper,EventMessage.class);
  }

and the route:

public void configure() throws Exception {
    from("kafka:localhost:9092?topic=item-events" +
            "&groupId=aggregator-group-id&autoCommitIntervalMs=25000&autoOffsetReset=earliest&consumersCount=1")
            .routeId("kafkapoller")
            .unmarshal(jacksonDataFormat)
            .aggregate(body().method("getItemId"), new EventAggregationStrategy()).completionInterval(20000)
            .marshal().json(JsonLibrary.Jackson)
            .to("kafka:localhost:9092?topic=item-events-aggregated&serializerClass=org.apache.kafka.common.serialization.ByteArraySerializer");
  }

Answer 1

This looks ok. Things to keep in mind:

• What happens if/when the JVM dies half way through an aggregation cycle? Dont care, then cool otherwise you may want to investigate the PersistentAggregationRepository to store/replay messages, although you can replay the messages you lost from kafka (this would be my biggest operational concern)
• Following on, think about runtime control. Camel is a shocker for not really telling you very clearly what's going at runtime. Things like runaway methods in your Aggregator (ie a very greedy regex) will leave you with little idea about the current state of the aggregated exchanges and JMX probably wont tell you too much about what's happening.
• I would use a AggregateController to enable you to externally force completion of the exchange, so you can do things like issue a shutdown to camel and then call this to complete the inflight exchange