#-#
#-# Annotations
#-#

#-# @HystrixCollapser

Property Default Description

collapserKey Name of annotated method Specifies a collapser key.
batchMethod - Method name of batch command which must have the following signature: java.util.List method(java.util.List).
scope Scope.REQUEST Defines what scope the collapsing should occur within.
collapserProperties {} Specifies collapser properties.

#-# @HystrixCommand

Property Default Description

groupKey Class name of annotated method Used for grouping together commands such as for reporting, alerting, etc.
commandKey Name of annotated method Hystrix command key
threadPoolKey - The thread-pool key is used to represent a HystrixThreadPool for monitoring, metrics publishing, caching and other such uses.
fallbackMethod - The method to process fallback logic which should be defined in the same class as the HystrixCommand.
commandProperties {} Specifies command properties
threadPoolProperties {} Specifies thread pool properties.
ignoreExceptions {} Defines exceptions which should be ignored and wrapped to throw in HystrixBadRequestException.

#-# @HystrixProperty

Property Default Description

name - Property name.
value - Property value.

#-# @CacheResult

Property Default Description

cacheKeyMethod - A method name to be used to get a key for request caching.

#-# @CacheRemove

Property Default Description

commandKey Name of annotated method The name of the Hystrix command for which the cache should be cleared.
cacheKeyMethod - A method name to be used to get a key for request caching.

#-# @CacheKey

Property Default Description

value - Allows to specify the name of a certain argument property.

#-#
#-# Properties
#-#

#-# @HystrixCollapser.collapserProperties

Property Default Description

maxRequestsInBatch Int.MAX The max nr of requests allowed in a batch before this triggers a batch execution.
timerDelayInMilliseconds 10 The number of milliseconds after the creation of the batch that its execution is triggered.
requestCache.enabled true Indicates whether request caching is enabled for HystrixCollapser.execute() and HystrixCollapser.queue() invocations.

#-# @HystrixCommand.commandProperties

Execution

Property Default Description

execution.isolation.strategy THREAD The isolation strategy HystrixCommand.run() executes with.
execution.isolation.thread.timeoutInMilliseconds 1000 The time in milliseconds after which the caller will observe a timeout and walk away from the command execution.
execution.timeout.enabled true Indicates whether the HystrixCommand.run() execution should have a timeout.
execution.isolation.thread.interruptOnTimeout true Indicates whether the HystrixCommand.run() execution should be interrupted when a timeout occurs.
execution.isolation.semaphore.maxConcurrentRequests 10 Max nr of requests allowed to a HystrixCommand.run() method when using ExecutionIsolationStrategy.SEMAPHORE.

Fallback

Property Default Description

fallback.isolation.semaphore.maxConcurrentRequests 10 The max nr of requests a HystrixCommand.getFallback() method is allowed to make from the calling thread.
fallback.enabled true Determines whether a call to HystrixCommand.getFallback() will be attempted when failure or rejection occurs.

Circuit Breaker

Property Default Description

circuitBreaker.enabled true Determines whether a circuit breaker will be used to track health and to short-circuit requests if it trips.
circuitBreaker.requestVolumeThreshold 20 The minimum number of requests in a rolling window that will trip the circuit.
circuitBreaker.sleepWindowInMilliseconds 5000 The amount of time, after tripping the circuit, to reject requests before allowing attempts again to determine if the circuit should again be closed.
circuitBreaker.errorThresholdPercentage 50 The error percentage at or above which the circuit should trip open and start short-circuiting requests to fallback logic.
circuitBreaker.forceOpen false Forces the circuit breaker into an open (tripped) state in which it will reject all requests. Takes precedence over circuitBreaker.forceClosed.
circuitBreaker.forceClosed false Forces the circuit breaker into a closed state in which it will allow requests regardless of the error percentage.

Metrics

Property Default Description

metrics.rollingStats.timeInMilliseconds 10000 The duration of the statistical rolling window, in milliseconds. This is how long Hystrix keeps metrics for the circuit breaker to use and for publishing.
metrics.rollingStats.numBuckets 10 The number of buckets the rolling statistical window is divided into.
metrics.rollingPercentile.enabled true Indicates whether execution latencies should be tracked and calculated as percentiles.
metrics.rollingPercentile.timeInMilliseconds 60000 The duration of the rolling window in which execution times are kept to allow for percentile calculations
metrics.rollingPercentile.numBuckets 6 The number of buckets the rollingPercentile window will be divided into.
metrics.rollingPercentile.bucketSize 100 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.
metrics.healthSnapshot.intervalInMilliseconds 500 The time to wait between allowing health snapshots to be taken that calculate success and error percentages and affect circuit breaker status.

Request Context

Property Default Description

requestCache.enabled true Indicates whether HystrixCommand.getCacheKey() should be used with HystrixRequestCache to provide de-duplication functionality via request-scoped caching.
requestLog.enabled true Indicates whether HystrixCommand execution and events should be logged to HystrixRequestLog

#-# @HystrixCommand.threadPoolProperties

Property Default Description

coreSize 10 The maximum number of HystrixCommands that can execute concurrently.
maxQueueSize -1 The maximum queue size of the BlockingQueue implementation. If you set this to -1 then SynchronousQueue will be used, otherwise a positive value will be used with LinkedBlockingQueue.
queueSizeRejectionThreshold 5 The queue size rejection threshold — an artificial maximum queue size at which rejections will occur even if maxQueueSize has not been reached.
keepAliveTimeMinutes 1 The keep-alive time.
metrics.rollingStats.timeInMilliseconds 10000 The duration of the statistical rolling window. This is how long metrics are kept for the thread pool.
metrics.rollingStats.numBuckets 10 The number of buckets the rolling statistical window is divided into.

#-#
#-# Examples
#-#

#-# Commands

Synchronous Execution

@HystrixCommand(groupKey=“UserGroup”, commandKey = “GetUserByIdCommand”)
public User getUserById(String id) {
return userResource.getUserById(id);
}

Asynchronous Execution

@HystrixCommand
public Future getUserByIdAsync(final String id) {
return new AsyncResult() {
@Override
public User invoke() {
return userResource.getUserById(id);
}
};
}

Reactive Execution

@HystrixCommand
public Observable getUserById(final String id) {
return new ObservableResult() {
@Override
public User invoke() {
return userResource.getUserById(id);
}
};
}

Fallback

@HystrixCommand(fallbackMethod = “defaultUser”)
public User getUserById(String id) {
return userResource.getUserById(id);
}
@HystrixCommand(fallbackMethod = “defaultUserSecond”)
private User defaultUser(String id) {
return new User();
}
@HystrixCommand
private User defaultUserSecond(String id) {
return new User(“def”, “def”);
}

Error Propagation

@HystrixCommand(ignoreExceptions = {BadRequestException.class})
public User getUserById(String id) {
return userResource.getUserById(id);
}

#-# Configuration

Command Properties

@HystrixCommand(
commandProperties = {
@HystrixProperty(name = “execution.isolation.thread.timeoutInMilliseconds”, value = “500”)
},
threadPoolProperties = {
@HystrixProperty(name = “coreSize”, value = “30”),
@HystrixProperty(name = “maxQueueSize”, value = “101”),
@HystrixProperty(name = “keepAliveTimeMinutes”, value = “2”),
@HystrixProperty(name = “queueSizeRejectionThreshold”, value = “15”),
@HystrixProperty(name = “metrics.rollingStats.numBuckets”, value = “12”),
@HystrixProperty(name = “metrics.rollingStats.timeInMilliseconds”, value = “1440”)
}
)
public User getUserById(String id) {
return userResource.getUserById(id);
}

Hystrix collapser

@HystrixCollapser(batchMethod = “getUserByIds”)
public Future getUserById(String id) {
return null;
}
@HystrixCommand
public List getUserByIds(List ids) {
List users = new ArrayList();
for (String id : ids) {
users.add(new User(id, “name: " + id));
}
return users;
}
Future f1 = userService.getUserById(“1”);
Future f2 = userService.getUserById(“2”);
Future f3 = userService.getUserById(“3”);
Future f4 = userService.getUserById(“4”);
Future f5 = userService.getUserById(“5”);

#-# Caching

Cache key generator

@CacheResult(cacheKeyMethod = “getUserByNameCacheKey”)
@HystrixCommand
public User getUserByName(String name) {
return storage.getByName(name);
}
private Long getUserByNameCacheKey(String name) {
return name;
}

Get-Set-Get pattern

@CacheResult
@HystrixCommand
public User getUserById(@CacheKey String id) { // GET
return storage.get(id);
}
@CacheRemove(commandKey = “getUserById”)
@HystrixCommand
public void update(@CacheKey(“id”) User user) { // SET
storage.put(user.getId(), user);
}

#-#
#-# References
#-#

[01] https://github.com/Netflix/Hystrix/wiki
[02] https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-javanica