THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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If you are proxying and load balancing HTTP, then see this page for more details.
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The round robin load balancer is stateful as it keeps state of which endpoint to use next time.
Using the Fluent BuildersWiki Markup
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The above example loads balance requests from direct:start to one of the available mock endpoint instances, in this case using a round robin policy.
For further examples of this pattern look at this junit test case
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The failover load balancer is capable of trying the next processor in case an Exchange failed with an exception during processing.
You can constrain the failover to activate only when one exception of a list you specify occurs. If you do not specify a list any exception will cause fail over to occur. This balancer uses the same strategy for matching exceptions as the Exception Clause does for the onException.
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If you use streaming then you should enable Stream caching when using the failover load balancer. This is needed so the stream can be re-read after failing over to the next processor.
Failover offers the following options:
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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.
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In Camel 2.2 or older the failover load balancer requires you have enabled Camel Error Handler to use redelivery. In 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:Wiki Markup
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Using failover in Spring DSL
Failover can also be used from Spring DSL and you configure it as:
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Using failover in round robin mode
An example using Java DSL:Wiki Markup Wiki Markup
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You can configure inheritErrorHandler=false if you want to failover to the next endpoint as fast as possible. By disabling the Error Handler you ensure it does not intervene which allows the failover load balancer to handle failover asap. By also enabling roundRobin mode, then it will keep retrying until it success. You can then configure the maximumFailoverAttempts option to a high value to let it eventually exhaust (give up) and fail.
Weighted Round-Robin and Random Load Balancing
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The weighted load balancing policy allows you to specify a processing load distribution ratio for each server with respect to others. You can specify this as a positive processing weight for each server. A larger number indicates that the server can handle a larger load. The weight is utilized to determine the payload distribution ratio to different processing endpoints with respect to others.
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As of Camel 2.6, the Weighted Load balancer usage has been further simplified, there is no need to send in distributionRatio as a List<Integer>. It can be simply sent as a delimited String of integer weights separated by a delimiter of choice.
The parameters that can be used are
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An example using Java DSL:
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And the same example using Spring XML:
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Available In Camel 2.6
An example using Java DSL:
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And the same example using Spring XML:
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Custom Load Balancer
You can use a custom load balancer (eg your own implementation) also.
An example using Java DSL:Wiki Markup Wiki Markup
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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
Circuit Breaker
The Circuit Breaker load balancer is a stateful pattern that monitors all calls for certain exceptions. Initially the Circuit Breaker is in closed state and passes all messages. If there are failures and the threshold is reached, it moves to open state and rejects all calls until halfOpenAfter timeout is reached. After this timeout is reached, if there is a new call, it will pass and if the result is success the Circuit Breaker will move to closed state, or to open state if there was an error.
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An example using Java DSL:
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And the same example using Spring XML:
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