Load Balancer

Overview

The load balancer pattern allows you to delegate message processing to one of several endpoints, using a variety of different load-balancing policies.

Java DSL example

The following route distributes incoming messages between the target endpoints, mock:x, mock:y, mock:z, using a round robin load-balancing policy:

from("direct:start").loadBalance().roundRobin().to("mock:x", "mock:y", "mock:z");

XML configuration example

The following example shows how to configure the same route in XML:

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <loadBalance>
        <roundRobin/>
        <to uri="mock:x"/>
        <to uri="mock:y"/>
        <to uri="mock:z"/>
    </loadBalance>
  </route>
</camelContext>

	Note
	In versions of FUSE Mediation Router earlier than 1.4.2.0, the `<roundRobin/>` tag must appear as the last tag inside the `loadBalance` element.

Load-balancing policies

The FUSE Mediation Router load balancer supports the following load-balancing policies:

Round robin

The round robin load-balancing policy cycles through all of the target endpoints, sending each incoming message to the next endpoint in the cycle. For example, if the list of target endpoints is, mock:x, mock:y, mock:z, then the incoming messages are sent to the following sequence of endpoints: mock:x, mock:y, mock:z, mock:x, mock:y, mock:z, and so on.

You can specify the round robin load-balancing policy in Java DSL, as follows:

from("direct:start").loadBalance().roundRobin().to("mock:x", "mock:y", "mock:z");

Alternatively, you can configure the same route in XML, as follows:

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <loadBalance>
        <roundRobin/>
        <to uri="mock:x"/>        
        <to uri="mock:y"/>       
        <to uri="mock:z"/>          
    </loadBalance>
  </route>
</camelContext>

Random

The random load-balancing policy chooses the target endpoint randomly from the specified list.

You can specify the random load-balancing policy in Java DSL, as follows:

from("direct:start").loadBalance().random().to("mock:x", "mock:y", "mock:z");

Alternatively, you can configure the same route in XML, as follows:

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <loadBalance>
        <random/>
        <to uri="mock:x"/>        
        <to uri="mock:y"/>       
        <to uri="mock:z"/>          
    </loadBalance>
  </route>
</camelContext>

Sticky

The sticky load-balancing policy directs the In message to an endpoint that is chosen by calculating a hash value from a specified expression. The advantage of this load-balancing policy is that expressions of the same value are always sent to the same server. For example, by calculating the hash value from a header that contains a username, you ensure that messages from a particular user are always sent to the same target endpoint. Another useful approach is to specify an expression that extracts the session ID from an incoming message. This ensures that all messages belonging to the same session are sent to the same target endpoint.

You can specify the sticky load-balancing policy in Java DSL, as follows:

from("direct:start").loadBalance().sticky(header("username")).to("mock:x", "mock:y", "mock:z");

Alternatively, you can configure the same route in XML, as follows:

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <loadBalance>
      <sticky>
        <expression>
          <simple>header.username</simple>
        </expression>
      </sticky>
      <to uri="mock:x"/>        
      <to uri="mock:y"/>       
      <to uri="mock:z"/>          
    </loadBalance>
  </route>
</camelContext>

Topic

The topic load-balancing policy sends a copy of each In message to all of the listed destination endpoints (effectively broadcasting the message to all of the destinations, like a JMS topic).

You can use the Java DSL to specify the topic load-balancing policy, as follows:

from("direct:start").loadBalance().topic().to("mock:x", "mock:y", "mock:z");

Alternatively, you can configure the same route in XML, as follows:

<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="direct:start"/>
    <loadBalance>
        <topic/>
        <to uri="mock:x"/>        
        <to uri="mock:y"/>       
        <to uri="mock:z"/>          
    </loadBalance>
  </route>
</camelContext>