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 to use this EIP:

Configuration Options

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

Name

Default Value

Type

Description

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.

commandKey

Node id

String

Used to identify the hystrix command. This option cannot be configured but is locked down to be the node id to make the command unique.

corePoolSize

10

Integer

This property sets the core thread-pool size. This is the maximum number of HystrixCommands that can execute concurrently.

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 timeout in milliseconds for execution completion.

executionTimeoutEnabled

true

Boolean

This property indicates whether the execution of HystrixCommand.run() should be timed.

fallbackEnabled

true

Boolean

This property determines whether a call to HystrixCommand.getFallback() will be attempted when failure or rejection occurs.

fallbackIsolationSemaphoreMaxConcurrentRequests

10

Integer

This property sets the maximum number of requests a HystrixCommand.getFallback() method is allowed to make from the calling thread.

groupKey

CamelHystrix

String

Used to identify the hystrix group being used by the EIP to correlate statistics, circuit-breaker, properties, etc.

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.

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 latency should be tracked. The latency is calculated as a percentile. If false summary statistics (mean, percentiles) are returned as -1.

metricsRollingPercentileWindowBuckets

6

Integer

This property sets the number of buckets the rollingPercentile window will be divided into.

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.

metricsRollingStatisticalWindowBuckets

10

Integer

This property sets the number of buckets the rolling statistical window is divided into.

metricsRollingStatisticalWindowInMilliseconds

10000

Integer

The following properties are related to capturing metrics from HystrixCommand and HystrixObservableCommand execution.

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.

requestLogEnabled

true

Boolean

This property indicates whether HystrixCommand execution and events should be logged to HystrixRequestLog.

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.

threadPoolMetricsRollingStatisticalWindowBuckets

10

Integer

This property sets the number of buckets the rolling statistical window is divided into.

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.

 

Example

Below is an example route showing an Hystrix endpoint that protects against slow operation by falling back to the in-lined fallback route. By default the timeout request is just 1000ms so the HTTP endpoint has to be fairly quick to succeed.

And in XML DSL:

onFallback vs onFallbackViaNetwork

If you are using onFallback then that is intended to be local processing only where you can do a message transformation or call a bean or something as the fallback. If you need to call an external service over the network then you should use onFallbackViaNetwork that runs in another independent HystrixCommand that uses its own thread pool to not exhaust the first command.

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.

 

And in XML DSL:

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

 

Example

You can find an example in the source code: camel-example-hystrix.

© 2004-2015 The Apache Software Foundation.
Apache Camel, Camel, Apache, the Apache feather logo, and the Apache Camel project logo are trademarks of The Apache Software Foundation. All other marks mentioned may be trademarks or registered trademarks of their respective owners.
Graphic Design By Hiram