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 |
---|---|---|---|
commandKey | node id | String | Used to identify the hystrix command instance being used by the EIP to correlate statistics, circuit-breaker, properties, etc. By default this will be derived from the node id. |
threadPoolKey | null | String | Used to define which thread-pool this command should run in. By default this is using the same key as the command key. |
cacheKey | null | Expression | Specifies the cache key to use from the given expression. |
initializeRequestContext | false | Boolean | When true, Camel will initialize a HystrixRequestContext during producer startup and use it for request scoped caching and request scoped logging. |
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:
|
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. |
requestCacheEnabled | true | Boolean | This property indicates whether HystrixCommand.getCacheKey() should be used with HystrixRequestCache to provide de-duplication functionality via request-scoped caching. |
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>