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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.

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.

Camel 2.x behavior
The round robin load balancer is not meant to work with failover, for that you should use the dedicated failover load balancer. The round robin load balancer will only change to next endpoint per message.

The round robin load balancer is statefull as it keeps state which endpoint to use next time.

Using the Fluent Builders

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

Using the Spring configuration

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language	xml

...

or

Code Block

language	xml

<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="direct:start"/>
    <loadBalance>        
        <roundRobin/>  <!-- This only support for Camel 1.5 -->
        <to uri="mock:x"/>        
        <to uri="mock:y"/>       
        <to uri="mock:z"/>                 
    </loadBalance>
  </route>
</camelContext>

...

Available as of Camel 2.0
The failover load balancer is capable of trying the next processor in case an Exchange failed with an exception during processing.
You can configure the failover with a list of specific exception to only failover. If you do not specify any exceptions it will failover over any exceptions. It uses the same strategy for matching exceptions as the Exception Clause does for the onException.

It has the following options:

Option	Type	Default	Description
inheritErrorHandler	boolean	true	Camel 2.3: Whether or not the Error Handler configured on the route should be used or not. You can disable it if you want the failover to trigger immediately and failover to the next endpoint. On the other hand if you have this option enabled, then Camel will first let the Error Handler try to process the message. The Error Handler may have been configured to redelivery and use delays between attempts. If you have enabled a number of redeliveries then Camel will try to redeliver to the same endpoint, and only failover to the next endpoint, when the Error Handler is exhausted.
maximumFailoverAttempts	int	-1	Camel 2.3: A value to indicate after X failver attempts we should exhaust (give up). Use -1 to indicate newer give up and always try to failover. Use 0 to newer failover. And use e.g. 3 to failover at most 3 times before giving up. This option can be used whether or not round robin is enabled or not.
roundRobin	boolean	false	Camel 2.3: Whether or not the `failover` load balancer should operate in round robin mode or not. If not, then it will always start from the first endpoint when a new message is to be processed. In other words it restart from the top for every message. If round robin is enabled, then it keeps state and will continue with the next endpoint in a round robin fashion. When using round robin it will not stick to last known good endpoint, it will always pick the next endpoint to use.

Camel 2.2 or older behavior
The current implement of failover load balancer is a simple logic which always tries the first endpoint, and in case of an exception being thrown it tries the next in the list, and so forth. It has no state, and the next message will thus always start with the first endpoint.

Camel 2.3 onwards behavior
The failover load balancer now supports round robin mode, which allows you to failover in a round robin fashion. See the roundRobin option.

Note

title	Redelivery must be enabled

The In Camel 2.2 or older the failover load balancer requires you have enabled Camel Error Handler to use redelivery. By default Camel does not do thisIn Camel 2.3 onwards this is not required as such, as you can mix and match. See the inheritErrorHandler option.

Here is a sample to failover only if a IOException related exception was thrown:

...

Code Block

	xml
	xml

   <route errorHandlerRef="myErrorHandler">
      <from uri="direct:foo"/>
      <loadBalance>
          <failover>
              <exception>java.io.IOException</exception>
              <exception>com.mycompany.MyOtherException</exception>
          </failover>
          <to uri="direct:a"/>
          <to uri="direct:b"/>
      </loadBalance>
    </route>

Using failover in round robin mode

An example using Java DSL:

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

And the same example using Spring XML:

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

Include Page

	CAMEL:Using This Pattern
	CAMEL:Using This Pattern

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Old Version 17

New Version 18

Key

Round Robin

Using failover in round robin mode