How publish event for more instance from command side axon - spring-boot

Question

I tried to implement application with cqrs and event sourcing with axon framework. I implement command side and query part as a separate micro-service and replicate(scale up) query micro-service. I use message broker as RabbitMq. If the command part publish event that not update all query micro-service. It work as round robin way. how can i update all micro-services same time.
Here is my dependency file
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-amqp</artifactId>
</dependency>
<dependency>
<groupId>org.axonframework</groupId>
<artifactId>axon-amqp</artifactId>
<version>${axon.version}</version>
</dependency>
<dependency>
<groupId>org.axonframework</groupId>
<artifactId>axon-spring-boot-starter</artifactId>
<version>${axon.version}</version>
</dependency>
this is my configs in command side
#Bean
public Exchange exchange() {
return ExchangeBuilder.fanoutExchange("SeatReserveEvents").build();
}
#Bean
public Queue queue() {
return QueueBuilder.durable("SeatReserveEvents").build();
}
#Bean
public Binding binding() {
return BindingBuilder.bind(queue()).to(exchange()).with("*").noargs();
}
#Autowired
public void configure(AmqpAdmin admin) {
admin.declareExchange(exchange());
admin.declareQueue(queue());
admin.declareBinding(binding());
}
This is application.yml
axon:
amqp:
exchange: SeatReserveEvents
This is command side configurations
#Bean
public SpringAMQPMessageSource statisticsQueue(Serializer serializer) {
return new SpringAMQPMessageSource(new DefaultAMQPMessageConverter(serializer)) {
#RabbitListener(queues = "SeatReserveEvents")
#Override
public void onMessage(Message arg0, Channel arg1) throws Exception {
super.onMessage(arg0, arg1);
}
};
}
this is handler
#Component
#ProcessingGroup("statistics")
public class EventLoggingHandler
{
#EventHandler
protected void on(SeatResurvationCreateEvent event) {
System.err.println(event);
}
#EventHandler
protected void on(SeatReservationUpdateEvent event) {
System.err.println(event);
}
}
this is application.yml
axon:
eventhandling:
processors:
statistics.source: statisticsQueue

Answer 1

I'd say this is more an AMQP/RabbitMQ configuration setting than an Axon Framework specific question. That said, you'd want to set up RabbitMQ to not do Round Robin, but Pub/Sub, like described in this tutorial here.
I do however have another, more Axon Framework specific response in mind.
Why immediately publish your events on a queue, if you could also pull the events from the store directly? So, you'd have TrackingEventProcessors on the Query Side of you application, which pull events from the event store as they get appended by the Command Side of your application.
That's how a monolith version of an Axon Framework application incorporating CQRS would initially look like any way. Hence the simplest next step to split up that CQRS application in a Command and Query side, would be to leave the way of receiving events as is, without adding the queue in between.
If you've got specific requirements to publish over a queue however, or you just prefer to use a queue instead of letting the Query applications pull from the Event Store directly, please disregard this comment and revert back to the RabbitMQ tutorial.

Answer 2

we need to change RabbitMq configuration to publish event for more instance from command side axon. For that we have to change configuration in publisher side as below.
#Bean
public FanoutExchange fanoutExchange() {
FanoutExchange exchange = new FanoutExchange("SeatReserveEvents");
return exchange;
}
#Autowired
public void configure(AmqpAdmin admin) {
admin.declareExchange(fanoutExchange());
}
and next thing is subscriber side we have to change bean like below
#Bean
public SpringAMQPMessageSource statisticsQueue(Serializer serializer) {
return new SpringAMQPMessageSource(new DefaultAMQPMessageConverter(serializer)) {
#RabbitListener(bindings = #QueueBinding(
value = #Queue,
exchange = #Exchange(value ="SeatReserveEvents",type = ExchangeTypes.FANOUT),
key = "orderRoutingKey")
)
#Override
public void onMessage(Message arg0, Channel arg1) throws Exception {
super.onMessage(arg0, arg1);
}
};
}
now we can replicate consumer for more instance. This pattern is publisher/subscriber pattern. and exchange type is fanout