Load Balance for Existing Messaging Service

This is a sample to show how we can change our existing messaging service for requirement or improvement. Here we use a load balance support as example.

Build the sample

Imagine that we have a message handling system built before to collect some information from our client and then process and record them. This scenario can be constructed by using the following XML route configuration.

<route>
  <from uri="file:src/data?noop=true"/>
      
  <!-- Print the message to standard out, just as a test -->
  <convertBodyTo type="java.lang.String"/>
  <to uri="stream:out"/> 
      
  <to uri="activemq:personnel.records"/>
</route>

<route>
  <from uri="activemq:personnel.records"/>
  <choice>
     <when>
       <xpath>/person/city = 'London'</xpath>
       <to uri="file:target/messages/uk"/>
     </when>
     <otherwise>
       <to uri="file:target/messages/others"/>
     </otherwise>
  </choice>
 </route>

For more instruction to build your sample, read the Camel Maven Archetypes page. The above routes are the default configuration for your new sample, so you can get started with it easily.
In this scenario, the first route is responsible to collect data from a directory: src/data, print it to standard output console and deliver it to a message queue to further processing. Then, another route get messages from the queue, and use Content Based Router to sort out them. The messages for person in London are stored in the directory: target/messages/uk, and others in target/messages/others. You can run this sample using command:

mvn jetty:run-war

After started, we can view the routes configured in camel context by directing your browser to http://localhost:8080/routes.

There are originally several message files in the directory: src/data and the message system processes them once it is started. We can get the processing result by checking the console and the files in target/messages.

Use Web Console to add load balance support

For a handful of small messages, one queue is enough to handle. But when encountering high volumn message input, we may want to use several queues to provide a load balance mechanism. So we can use the camel Load Balancer support. The messaging service improvement here is much easier than that in other messaging system. You can open the routes on the above page.

Use a loadBalance DSL for the message delivery on route1:

from("file:src/data?noop=true").convertBodyTo(java.lang.String.class).to("stream:out")
  .loadBalance().random()
    .to("activemq:personnel.records1")
    .to("activemq:personnel.records2")
  .end()

Let the route2 collect messages from both queues providing the load balance support:

from("activemq:personnel.records1", "activemq:personnel.records2")
  .choice()
    .when().xpath("/person/city = 'London'").to("file:target/messages/uk")
    .otherwise().to("file:target/messages/others")
  .end()

With these two operations, you have complete this work. Just throw your message into the directory, camel will process and deliver it automatically. By the way, you may need some Dead Letter Channel configuration for it since XML analyzing with rigid format usually accompanies frequent error.