Circuit breakers for Java: Failsafe, Javaslang-Circuitbreaker, Hystrix and Vert.x
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The document provides an overview of circuit breakers in Java, discussing their states (closed, open, half-open) and how they manage failures in remote APIs to maintain application resilience. It includes implementations using libraries like Failsafe, Javaslang, Netflix Hystrix, and Vert.x, along with sample code for each. The focus is on ensuring resources are efficiently utilized and recovery is facilitated in overloaded systems.
Circuit breakers for Java: Failsafe, Javaslang-Circuitbreaker, Hystrix and Vert.x
- 1. Micha Kops www.hascode.com 1 Article on hasCode.com Circuit Breakers for Java: Failsafe, Javaslang-CB, Hystrix and Vert.x Resilient Architecture in Practice
- 2. Micha Kops www.hascode.com 2 Article on hasCode.com Why? ● Remote-APIs might hang / have latency issues / throw exceptions / behave unresponsive ● Our application blocks resources, allocates memory for threads and bound objects ● Spamming requests to an overloaded remote API might prevent its recovery
- 3. Micha Kops www.hascode.com 3 Article on hasCode.com States
- 4. Micha Kops www.hascode.com 4 Article on hasCode.com Closed-State ● The circuit-breaker executes operations as usual ● If a failure occurs, the circuit-breaker writes it down ● If a specified error threshold (number of failures or frequency of failures) is reached, it trips and opens the circuit (transitions to the open-state)
- 5. Micha Kops www.hascode.com 5 Article on hasCode.com Open-State ● Calls to the circuit-breaker in the open state fail immediately ● No call to the underlying operation is executed ● After a specified timeout is reached, the circuit- breaker transitions to the half-open state.
- 6. Micha Kops www.hascode.com 6 Article on hasCode.com Half-Open-State ● In this state, one call is allowed to call the underlying operation ● If this call fails, the circuit-breaker transitions to the open-state again until another timeout is reached ● If it succeeds, the circuit-breaker resets and transitions to the closed-state.
- 7. Micha Kops www.hascode.com 7 Article on hasCode.com Implementations for Java ● Failsafe ● Javaslang-Circuitbreaker ● Netflix Hystrix ● Vert.x Circuitbreaker
- 8. Micha Kops www.hascode.com 8 Article on hasCode.com Failsafe - Example UnstableApplication app = new UnstableApplication(); CircuitBreaker breaker = new CircuitBreaker().withFailureThreshold(2).withSuccessThreshold(5).withDelay(1, TimeUnit.SECONDS); RetryPolicy retryPolicy = new RetryPolicy().withDelay(2, TimeUnit.SECONDS).withMaxDuration(60, TimeUnit.SECONDS) .withBackoff(4, 40, TimeUnit.SECONDS); System.out.printf("circuit-breaker state is: %sn", breaker.getState()); for (int i = 0; i < 10; i++) { Thread.sleep(1000); try { String id = Failsafe.with(breaker).with(retryPolicy) .onFailedAttempt((a, b) -> System.err.printf( "failed with exception: '%s' at '%s', circuit-breaker state is: '%s'n", b, ZonedDateTime.now(), breaker.getState())) .onSuccess((a, b) -> System.out.printf("call succeeded, circuit-breaker state is: '%s'n", breaker.getState())) .get(app::generateId); System.out.printf("FailsafeExample: id '%s' received at '%s'n", id, ZonedDateTime.now()); } catch (CircuitBreakerOpenException e) { System.out.printf("circuit-breaker is open (state %s), time is '%s'n", breaker.getState(), ZonedDateTime.now()); } }
- 9. Micha Kops www.hascode.com 9 Article on hasCode.com Javaslang ExampleUnstableApplication app = new UnstableApplication(); CircuitBreakerConfig breakerConfig = CircuitBreakerConfig.custom().ringBufferSizeInClosedState(2) .ringBufferSizeInHalfOpenState(2).failureRateThreshold(50) .waitDurationInOpenState(Duration.ofMillis(1000)).build(); CircuitBreaker breaker = CircuitBreaker.of("unstableAppBreaker", breakerConfig); Try.CheckedSupplier<String> decoratedSupplier = Decorators.ofCheckedSupplier(app::generateId) .withCircuitBreaker(breaker).decorate(); System.out.printf("circuit-breaker state is: %sn", breaker.getState()); for (int i = 0; i < 10; i++) { Thread.sleep(1000); Try<String> result = Try.of(decoratedSupplier) .onSuccess((a) -> System.out.printf("call succeeded, circuit- breaker state is: '%s'n", breaker.getState())) .onFailure(e -> System.err.printf( "failed with exception: '%s' at '%s', circuit-breaker state is: '%s'n", e, ZonedDateTime.now(), breaker.getState())); if (!result.isEmpty()) { System.out.printf("JavaslangExample: id '%s' received at '%s'n", result.get(), ZonedDateTime.now()); } }
- 10. Micha Kops www.hascode.com 10 Article on hasCode.com Hystrix Example (I) class IdGeneratingCommand extends HystrixObservableCommand<String> { private final UnstableApplication app; public IdGeneratingCommand(HystrixObservableCommand.Setter setter, UnstableApplication app) { super(setter); this.app = app; } @Override protected Observable<String> construct() { return Observable.create(observer -> { try { if (!observer.isUnsubscribed()) { observer.onNext(app.generateId()); observer.onCompleted(); } } catch (SampleException e) { observer.onError(e); } }); } };
- 11. Micha Kops www.hascode.com 11 Article on hasCode.com Hystrix Example (II)UnstableApplication app = new UnstableApplication(); HystrixObservableCommand.Setter setter = HystrixObservableCommand.Setter .withGroupKey(HystrixCommandGroupKey.Factory.asKey("unstableAppCmdGroup")) .andCommandPropertiesDefaults(HystrixCommandProperties.Setter().withCircuitBreakerEnabled(t rue) .withCircuitBreakerErrorThresholdPercentage(50) .withCircuitBreakerSleepWindowInMilliseconds(1000).withCircuitBreakerRequestVolumeThreshold (1)); for (int i = 0; i < 10; i++) { CountDownLatch l = new CountDownLatch(1); IdGeneratingCommand cmd = new IdGeneratingCommand(setter, app); final HealthCounts healthCounts = cmd.getMetrics().getHealthCounts(); System.out.printf("circuit-breaker state is open: %s, %d errors of %d requestsn", cmd.isCircuitBreakerOpen(), healthCounts.getErrorCount(), healthCounts.getTotalRequests()); Observable<String> observable = cmd.observe(); observable.subscribe(s -> { System.out.printf("HystrixExample: id '%s' received at '%s'n", s, ZonedDateTime.now()); } , t -> { System.err.printf("HystrixExample: error %s, circuit-breaker state is open: %sn", t, cmd.isCircuitBreakerOpen()); } , () -> { l.countDown(); }); l.await(4, TimeUnit.SECONDS); }
- 12. Micha Kops www.hascode.com 12 Article on hasCode.com Vert.x ExampleUnstableApplication app = new UnstableApplication(); Vertx vertx = Vertx.vertx(); CircuitBreaker breaker = CircuitBreaker .create("unstableAppBreaker", vertx, new CircuitBreakerOptions().setMaxFailures(2).setTimeout(2000).setFallbackOnFailure(true) .setResetTimeout(2000)) .openHandler(h -> System.err.println("circuit-breaker opened")) .closeHandler(h -> System.out.println("circuit-breaker closed")) .halfOpenHandler(h -> System.err.println("circuit-breaker half-opened")); System.out.printf("circuit-breaker state is: %sn", breaker.state()); for (int i = 0; i < 10; i++) { Thread.sleep(1000); breaker.<String> execute(future -> { try { final String id = app.generateId(); future.complete(id); } catch (SampleException e) { future.fail(e); } if (future.failed()) { System.err.printf("failed with exception: '%s' at '%s', circuit-breaker state is: '%s'n", future.cause(), ZonedDateTime.now(), breaker.state()); } }).setHandler(id -> { if (id.succeeded()) System.out.printf("VertxExample: id '%s' received at '%s'n", id, ZonedDateTime.now()); }); } vertx.close();
- 13. Micha Kops www.hascode.com 13 Article on hasCode.com The End Thanks for your audience