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Policy

Description

Round Robin

The exchanges is selected in a round robin fashion. This is a well known and classic policy. This spreads the load even.

Random

A random endpoint is selected for each exchange

Sticky

Sticky load balancing using an Expression to calculate a correlation key to perform the sticky load balancing; rather like jsessionid in the web or JMSXGroupID in JMS.

Topic

Topic which sends to all destinations (rather like JMS Topics)

Failover

Camel 2.0: In case of failures the exchange is tried on the next endpoint.

Weighted Round-Robin

Camel 2.5: The weighted load balancing policy allows you to specify a processing load distribution ratio for each server with respect to others.In addition to the weight, endpoint selection is then further refined using round-robin distribution based on weight.

Weighted Random

Camel 2.5: The weighted load balancing policy allows you to specify a processing load distribution ratio for each server with respect to others.In addition to the weight, endpoint selection is then further refined using random distribution based on weight.

Custom

Camel 2.8: From Camel 2.8 onwards the preferred way of using a custom Load Balancer is to use this policy, instead of using the @deprecated ref attribute.

Round Robin

Camel 1.x behavior
The round robin load balancer can actually be used to failover with Camel 1.x. This is no longer possible in Camel 2.x as the underlying Error Handler foundation has been significantly overhauled in Camel 2.x. Frankly the round robin load balancer in Camel 1.x was not thought to be used in a failover scenario.

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Code Block
xml
xml
    <route>
      <from uri="direct:start"/>
      <loadBalance>
        <weighted roundRobin="false" distributionRatio="4-2-1" distributionRatioDelimiter="-" />
          <to uri="mock:x"/>
          <to uri="mock:y"/>
          <to uri="mock:z"/>
      </loadBalance>
    </route>

Custom Load Balancer

You can use a custom load balancer (eg your own implementation) also.

An example using Java DSL:

Wiki Markup
{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/CustomLoadBalanceTest.java}

And the same example using XML DSL:

Wiki Markup
{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringCustomRefLoadBalanceTest.xml}

Notice in the XML DSL above we use <custom> which is only available in Camel 2.8 onwards. In older releases you would have to do as follows instead:

Code Block
xml
xml

      <loadBalance ref="myBalancer">
        <!-- these are the endpoints to balancer -->
        <to uri="mock:x"/>
        <to uri="mock:y"/>
        <to uri="mock:z"/>
      </loadBalance>

To implement a custom load balancer you can extend some support classes such as LoadBalancerSupport and SimpleLoadBalancerSupport. The former supports the asynchronous routing engine, and the latter does not. Here is an example:

Wiki Markup
{snippet:id=e2|title=Custom load balancer implementation|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/CustomLoadBalanceTest.java}
Include Page
CAMEL:Using This Pattern
CAMEL:Using This Pattern