Intro to Hystrix

May 27, 2015 2-minute read

citytechinc • hystrix • java

What is Hystrix?

Hystrix is a latency and fault tolerance library designed by Netflix to isolate, primarily, points of access remote systems, services, and 3rd party libraries. Hystrix prevents cascading failures and enables resiliency in complex distributed systems where failure is considered inevitable.

What Hystrix provides

Hystrix aims to enable a system to handle unexpected, external situations, allow for service availability scale back or service degradation in a systematic, controlled manner.

Applied Patterns

Timeout
Circuit Breaker
Load Shedder
Fallback

Advanced Features

Request Caching
Request Collapsing
Plugins
Dashboard

Basic Usage

public class CommandHelloWorld extends HystrixCommand<String> {

  private final String name;

  public CommandHelloWorld(String name) {
    super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"));
    this.name = name;
  }

  @Override
  protected String run() {
    // a real example would do work like a network call here
    return "Hello " + name + "!";
  }
}

Sync, Blocking Usage

String s = new CommandHelloWorld("World").execute();

@Test
public void testSynchronous() {
  assertEquals("Hello World!", new CommandHelloWorld("World").execute());
  assertEquals("Hello Bob!", new CommandHelloWorld("Bob").execute());
}

Async, Non-blocking Usage

Future<String> fs = new CommandHelloWorld("World").queue();

@Test
public void testAsynchronous1() throws Exception {
  assertEquals("Hello World!", new CommandHelloWorld("World").queue().get());
  assertEquals("Hello Bob!", new CommandHelloWorld("Bob").queue().get());
}

RxJava, Reactive Streams Usage

Observable<String> ho = new CommandHelloWorld("World").observe();

ho.subscribe(new Action1<String>() {

  @Override
  public void call(String s) {
  }
});

@Test
public void testObservable() throws Exception {

  Observable<String> fWorld = new CommandHelloWorld("World").observe();

  fBob.subscribe(new Action1<String>() {

    @Override
    public void call(String v) {
      System.out.println("onNext: " + v);
    }
  });
}

Basic Fallback Usage

public class CommandHelloWorld extends HystrixCommand<String> {

  private final String name;

  public CommandHelloWorld(String name) {
    super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"));
    this.name = name;
  }

  @Override
  protected String run() {
    // a real example would do work like a network call here
    return "Hello " + name + "!";
  }

  @Override
  protected String getFallback() {
    return "Hello Failure " + name + "!";
  }
}

Error Propagation

public class CommandHelloWorld extends HystrixCommand<String> {

  private final String name;

  public CommandHelloWorld(String name) {
    super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"));
    this.name = name;
  }

  @Override
  protected String run() {
    throw new HystrixBadRequestException("I fail differently",
      new RuntimeException("I will always fail"));
  }

  @Override
  protected String getFallback() {
    return "Hello Failure " + name + "!";
  }
}

Configuration Tweaks

Command Execution Isolation Strategy
Timeouts
Circuit Breaker Thresholds
Command Queue Sizes, Rejection Policies, etc…