Hystrix EIP

Available as of Camel 2.18

The hystrix EIP provides integration with Netflix Hystrix to be used as circuit breaker in the Camel routes. Hystrix is a latency and fault tolerance library designed to isolate points of access to remote systems, services and 3rd party libraries, stop cascading failure and enable resilience in complex distributed systems where failure is inevitable.

Maven users will need to add the following dependency to their pom.xml for this EIP:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-hystrix</artifactId>
    <version>x.x.x</version><!-- use the same version as your Camel core version -->
</dependency>

Configuration Options

The EIP supports the following options. The default values are coming from Hystrix itself.

Name	Default Value	Type	Description
groupKey	CamelHystrix	String	Used to identify the hystrix command instance being used by the EIP to correlate statistics, circuit-breaker, properties, etc.
threadPoolKey	null	String	Used to define which thread-pool this command should run in. By default this is using the same key as the group key.
corePoolSize	10	Integer	This property sets the core thread-pool size. This is the maximum number of HystrixCommands that can execute concurrently.
keepAliveTime	1	Integer	This property sets the keep-alive time, in minutes.
maxQueueSize	-1	Integer	This property sets the maximum queue size of the BlockingQueue implementation.
queueSizeRejectionThreshold	5	Integer	This property sets the queue size rejection threshold — an artificial maximum queue size at which rejections will occur even if maxQueueSize has not been reached.
threadPoolMetricsRollingStatisticalWindowInMilliseconds	10000	Integer	This property sets the duration of the statistical rolling window, in milliseconds. This is how long metrics are kept for the thread pool.
threadPoolMetricsRollingStatisticalWindowBuckets	10	Integer	This property sets the number of buckets the rolling statistical window is divided into.
circuitBreakerEnabled	true	Boolean	This property determines whether a circuit breaker will be used to track health and to short-circuit requests if it trips.
circuitBreakerErrorThresholdPercentage	50	Integer	This property sets the error percentage at or above which the circuit should trip open and start short-circuiting requests to fallback logic.
circuitBreakerForceClosed	false	Boolean	This property, if true, forces the circuit breaker into a closed state in which it will allow requests regardless of the error percentage.
circuitBreakerForceOpen	false	Boolean	This property, if true, forces the circuit breaker into an open (tripped) state in which it will reject all requests.
circuitBreakerRequestVolumeThreshold	20	Integer	This property sets the minimum number of requests in a rolling window that will trip the circuit.
circuitBreakerSleepWindowInMilliseconds	5000	Integer	This property sets the amount of time, after tripping the circuit, to reject requests before allowing attempts again to determine if the circuit should again be closed.
executionIsolationSemaphoreMaxConcurrentRequests	10	Integer	This property sets the maximum number of requests allowed to a HystrixCommand.run() method when you are using ExecutionIsolationStrategy.SEMAPHORE. If this maximum concurrent limit is hit then subsequent requests will be rejected.
executionIsolationStrategy	THREAD	String	This property indicates which isolation strategy HystrixCommand.run() executes with, one of the following two choices: THREAD — it executes on a separate thread and concurrent requests are limited by the number of threads in the thread-pool SEMAPHORE — it executes on the calling thread and concurrent requests are limited by the semaphore count
executionIsolationThreadInterruptOnTimeout	true	Boolean	This property indicates whether the HystrixCommand.run() execution should be interrupted when a timeout occurs.
executionTimeoutInMilliseconds	1000	Integer	This property sets the time in milliseconds after which the caller will observe a timeout and walk away from the command execution.
executionTimeoutEnabled	true	Boolean	This property indicates whether the HystrixCommand.run() execution should have a timeout.
fallbackIsolationSemaphoreMaxConcurrentRequests	10	Integer	This property sets the maximum number of requests a HystrixCommand.getFallback() method is allowed to make from the calling thread.
fallbackEnabled	true	Boolean	This property determines whether a call to HystrixCommand.getFallback() will be attempted when failure or rejection occurs.
metricsHealthSnapshotIntervalInMilliseconds	500	Integer	This property sets the time to wait, in milliseconds, between allowing health snapshots to be taken that calculate success and error percentages and affect circuit breaker status.
metricsRollingPercentileBucketSize	100	Integer	This property sets the maximum number of execution times that are kept per bucket. If more executions occur during the time they will wrap around and start over-writing at the beginning of the bucket.
metricsRollingPercentileEnabled	true	Boolean	This property indicates whether execution latencies should be tracked and calculated as percentiles. If they are disabled, all summary statistics (mean, percentiles) are returned as -1.
metricsRollingPercentileWindowInMilliseconds	60000	Integer	This property sets the duration of the rolling window in which execution times are kept to allow for percentile calculations, in milliseconds.
metricsRollingPercentileWindowBuckets	6	Integer	This property sets the number of buckets the rollingPercentile window will be divided into.
metricsRollingStatisticalWindowInMilliseconds	10000	Integer	The following properties are related to capturing metrics from HystrixCommand and HystrixObservableCommand execution.
metricsRollingStatisticalWindowBuckets	10	Integer	This property sets the number of buckets the rolling statistical window is divided into.
requestLogEnabled	true	Boolean	This property indicates whether HystrixCommand execution and events should be logged to HystrixRequestLog.

Example

Below is an example route that with Hystrix endpoint that protects agains slow operation and fallbacks to the inlined fallback route. By default the timeout request is just 1000 millis (1 sec) so the http endpoint has to be fairly quick to succeed.

from("direct:start")
    .hystrix()
        .to("http://fooservice.com/slow")
    .fallback()
        .transform().constant("Fallback message")
    .end()
    .to("mock:result");

And in XML DSL:

<camelContext xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="direct:start"/>
    <hystrix>
      <to uri="http://fooservice.com/slow"/>
      <fallback>
        <transform>
          <constant>Fallback message</constant>
        </transform>
      </fallback>
    </hystrix>
    <to uri="mock:result"/>
  </route>
</camelContext>

Configuring Hystrix Example

Hystrix has many options as listed in the table above. For example to set a higher timeout to 5 seconds, and also let the circuit breaker wait 10 seconds before attempting a request again when the state was tripped to be open.

from("direct:start")
    .hystrix()
        .configure()
             .executionTimeoutInMilliseconds(5000).circuitBreakerSleepWindowInMilliseconds(10000)
        .end()
        .to("http://fooservice.com/slow")
    .fallback()
        .transform().constant("Fallback message")
    .end()
    .to("mock:result");

And in XML DSL:

<camelContext xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="direct:start"/>
    <hystrix>
      <hystrixConfiguration executionTimeoutInMilliseconds="5000" circuitBreakerSleepWindowInMilliseconds="10000"/>
      <to uri="http://fooservice.com/slow"/>
      <fallback>
        <transform>
          <constant>Fallback message</constant>
        </transform>
      </fallback>
    </hystrix>
    <to uri="mock:result"/>
  </route>
</camelContext>

You can also configure hystrix globally and then refer to that configuration:

<camelContext xmlns="http://camel.apache.org/schema/spring">
 
  <!-- a shared config which you can refer to from all your hystrix EIPs -->
  <hystrixConfiguration id="sharedConfig" executionTimeoutInMilliseconds="5000" circuitBreakerSleepWindowInMilliseconds="10000"/>
 
  <route>
    <from uri="direct:start"/>
    <hystrix hystrixConfigurationRef="sharedConfig">
      <to uri="http://fooservice.com/slow"/>
      <fallback>
        <transform>
          <constant>Fallback message</constant>
        </transform>
      </fallback>
    </hystrix>
    <to uri="mock:result"/>
  </route>
</camelContext>

Child pages

Hystrix EIP

Hystrix EIP

Configuration Options

Example

Configuring Hystrix Example