By default, Elastic Path Commerce publishes event messages to ActiveMQ virtual destinations, which is also called Virtual Topics, with separate consumer queues for each function that wants to get the message. This method supports competing consumers, does not lose messages if subscribers are offline, and does not require configuration on ActiveMQ for both development and production.

The advantages of virtual destinations are decoupled publisher/subscriber architecture and reliable load-balancing of message processors.

The following example demonstrates a cluster of two identical integration servers, integration server1 and integration server 2, where each contains two JMS consumers A and B that subscribe to the order message channel:

To utilize virtual destinations, register each subscriber component within the Commerce Engine as an individual output queue within the virtual topic. For example, to accommodate the message consumer that creates order confirmation emails and the message consumer that creates order shipment confirmation emails, the order message channel is configured with a producer topic of VirtualTopic.ep.orders and multiple consumer queues including Consumer.orderconfirmationEmailHandler.VirtualTopic.ep.orders and Consumer.orderShipmentShippedEmailHandler.VirtualTopic.ep.orders. Each of these consumers exist as a JMS queue to which all messages on the VirtualTopic.ep.orders topic are published.

Be default, Elastic Path uses ActiveMQ default naming conventions to enable Virtual Destinations. For other messaging brokers, Virtual Destinations might need different configuration. For more information, see the documentation for the specific messaging broker.

The following table provides the default Elastic Path configuration of the event message channels to enable ActiveMQ Virtual Destinations:

If the JMS broker doesn't support virtual destinations, you can implement a recipient list consumer to replicate the functionality of virtual destinations. You must configure the recipient list with a list of the output JMS queue endpoints and publish all messages on the incoming queue to each of the required queues. In the following example, each recipient list consumer forwards every incoming message on the ep.orders queue to ep.orders.A and ep.orders.B queues.

For the recipient list consumer, follow the same configuration settings of virtual destinations as described in the virtual destinations section except for the producer URI by defining it as queues instead of topics. You can also remove the VirtualTopic and Consumer prefixes, because Elastic Path does not follow naming convention to define this functionality.

The following example describes a sample recipient list message forwarding route builder and its Spring XML configuration:

public class SampleRecipientListMessageForwardingRouteBuilder extends RouteBuilder {
 
	private Endpoint incomingEndpoint;
	private Collection<Endpoint> outgoingEndpoints;

	@Override
	public void configure() throws Exception {
		from(incomingEndpoint)
			.transacted()
			.to(outgoingEndpoints);
	}
 
	// getters and setters
 
}

<beans
        xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:camel="http://camel.apache.org/schema/spring"
		xmlns:util="http://www.springframework.org/schema/util"
        xsi:schemaLocation="
                http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
				http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.0.xsd
                http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd
        ">
 
    <camel:camelContext id="sample-recipient-list-forwarder" xmlns="http://camel.apache.org/schema/spring">
		<routeBuilder ref="sampleRecipientListMessageForwardingRouteBuilder"/commerce-legacy/>
    </camel:camelContext>
  
	<bean id="sampleRecipientListMessageForwardingRouteBuilder" class="com.example.SampleRecipientListMessageForwardingRouteBuilder">
		<property name="incomingEndpoint">
			<bean class="org.apache.camel.spring.CamelEndpointFactoryBean">
				<property name="camelContextId" value="sample-recipient-list-forwarder" />
				<property name="uri" value="jms:ep.eventmessagetype"/commerce-legacy/>
			</bean>
		</property>
		<property name="outgoingEndpoints">
			<util:list>
				<bean class="org.apache.camel.spring.CamelEndpointFactoryBean">
					<property name="camelContextId" value="sample-recipient-list-forwarder" />
					<property name="uri" value="jms:ep.eventmessagetype.Queue1"/commerce-legacy/>
				</bean>
				<bean class="org.apache.camel.spring.CamelEndpointFactoryBean">
					<property name="camelContextId" value="sample-recipient-list-forwarder" />
					<property name="uri" value="jms:ep.eventmessagetype.Queue2"/commerce-legacy/>
				</bean>
				<bean class="org.apache.camel.spring.CamelEndpointFactoryBean">
					<property name="camelContextId" value="sample-recipient-list-forwarder" />
					<property name="uri" value="jms:ep.eventmessagetype.Queue3"/commerce-legacy/>
				</bean>
				<!-- etc. -->
			</util:list>
		</property>
	</bean>
 
</beans>

The outgoing queues for each Commerce Engine event message channel are listed in the virtual destination configuration table.