How to manually control the offset commit with camel-kafka?

Question

I'm using the camel kafka component and I'm unclear what is happening under the hood with committing the offsets. As can be seen below, I'm aggregating records and I think for my use case that it only makes sense to commit the offsets after the records have been saved to SFTP.

Is it possible to manually control when I can perform the commit?

private static class MyRouteBuilder extends RouteBuilder {

    @Override
    public void configure() throws Exception {

        from("kafka:{{mh.topic}}?" + getKafkaConfigString())
        .unmarshal().string()
        .aggregate(constant(true), new MyAggregationStrategy())
            .completionSize(1000)
            .completionTimeout(1000)
        .setHeader("CamelFileName").constant("transactions-" + (new Date()).getTime())
        .to("sftp://" + getSftpConfigString())

        // how to commit offset only after saving messages to SFTP?

        ;
    }

    private final class MyAggregationStrategy implements AggregationStrategy {
        @Override
        public Exchange aggregate(Exchange oldExchange, Exchange newExchange) {
            if (oldExchange == null) {
                return newExchange;
            }
            String oldBody = oldExchange.getIn().getBody(String.class); 
            String newBody = newExchange.getIn().getBody(String.class);
            String body = oldBody + newBody;
            oldExchange.getIn().setBody(body);
            return oldExchange;
        }
    }
}

private static String getSftpConfigString() {
        return "{{sftp.hostname}}/{{sftp.dir}}?"
                + "username={{sftp.username}}"
                + "&password={{sftp.password}}"
                + "&tempPrefix=.temp."
                + "&fileExist=Append"
                ;
}

private static String getKafkaConfigString() {
        return "brokers={{mh.brokers}}" 
            + "&saslMechanism={{mh.saslMechanism}}"  
            + "&securityProtocol={{mh.securityProtocol}}"
            + "&sslProtocol={{mh.sslProtocol}}"
            + "&sslEnabledProtocols={{mh.sslEnabledProtocols}}" 
            + "&sslEndpointAlgorithm={{mh.sslEndpointAlgorithm}}"
            + "&saslJaasConfig={{mh.saslJaasConfig}}" 
            + "&groupId={{mh.groupId}}"
            ;
}

Answer 1

You can control manual offset commit even in multi threaded route (using aggregator for exemple) by using offset repository (Camel Documentation)

@Override
public void configure() throws Exception {
      // The route
      from(kafkaEndpoint())
            .routeId(ROUTE_ID)
            // Some processors...
            // Commit kafka offset
            .process(MyRoute::commitKafka)
            // Continue or not...
            .to(someEndpoint());
}

private String kafkaEndpoint() {
    return new StringBuilder("kafka:")
            .append(kafkaConfiguration.getTopicName())
            .append("?brokers=")
            .append(kafkaConfiguration.getBootstrapServers())
            .append("&groupId=")
            .append(kafkaConfiguration.getGroupId())
            .append("&clientId=")
            .append(kafkaConfiguration.getClientId())
            .append("&autoCommitEnable=")
            .append(false)
            .append("&allowManualCommit=")
            .append(true)
            .append("&autoOffsetReset=")
            .append("earliest")
            .append("&offsetRepository=")
            .append("#fileStore")
            .toString();

}

@Bean(name = "fileStore", initMethod = "start", destroyMethod = "stop")
private FileStateRepository fileStore() {
    FileStateRepository fileStateRepository = 
    FileStateRepository.fileStateRepository(new File(kafkaConfiguration.getOffsetFilePath()));
    fileStateRepository.setMaxFileStoreSize(10485760); // 10MB max

    return fileStateRepository;
}

private static void commitKafka(Exchange exchange) {
    KafkaManualCommit manual = exchange.getIn().getHeader(KafkaConstants.MANUAL_COMMIT, KafkaManualCommit.class);
    manual.commitSync();
}

Answer 2

I think this is change in the latest version of camel (2.22.0) (the doc) you should be able to do that.

// Endpoint configuration &autoCommitEnable=false&allowManualCommit=true
public void process(Exchange exchange) {
     KafkaManualCommit manual = exchange.getIn().getHeader(KafkaConstants.MANUAL_COMMIT, KafkaManualCommit.class);
     manual.commitSync();
}

Answer 3

No you cannot. Kafka performs an auto commit in the background every X seconds (you can configure this).

There is no manual commit support in camel-kafka. Also this would not be possible as the aggregator is separated from the kafka consumer, and its the consumer that performs the commit.