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提高 Liberty 中的微服务弹性
可以使用 MicroProfile 容错功能部件使服务调用更具弹性。此功能部件是 Eclipse Microprofile 容错规范 1.0 的实现。此功能部件使用 Failsafe 开放式源代码库提供一个编程模型,以通过包含重试、断路器、隔板、超时和回退的模式来支持有弹性的微服务。
开始之前
过程
- 将 mpFaultTolerance-1.0 功能部件添加至 server.xml 文件中的 featureManager 元素。
<featureManager> <feature>mpFaultTolerance-1.0</feature> </featureManager>
- 使用代码段来提高微服务的弹性。 容错断路器提供了一种使系统快速失败的方式。它会暂时禁止运行服务,以防止该服务使系统过载。容错 RetryPolicy 提供了一种配置何时重试服务的方式。容错回退可指定在主服务失败的情况下要使用的服务。容错隔板将限制服务的并发调用数。隔板将限制服务调用可以耗用的系统资源量。代码段要求除了在 server.xml 文件中指定 mpFaultTolerance-1.0 功能部件之外,还要指定 Liberty concurrent-1.0 功能部件。
断路器代码段 1:创建具有已配置的断路器和超时的 CircuitBreakerBean。
@RequestScoped public class CircuitBreakerBean { private int executionCounterA = 0; // The combined effect of the specified requestVolumeThreshold and failureRatio is that 3 // failures will trigger the circuit to open. // After a 1 second delay the Circuit will allow fresh attempts to invoke the service. @CircuitBreaker(delay = 1, delayUnit = ChronoUnit.SECONDS, requestVolumeThreshold = 3, failureRatio = 1.0) // A service is considered to have timed out after 3 seconds @Timeout(value = 3, unit = ChronoUnit.SECONDS) public String serviceA() { executionCounterA++; if (executionCounterA <= 3) { //Sleep for 10 secs to force a timeout try { Thread.sleep(10000); } catch (InterruptedException e) { System.out.println("serviceA interrupted"); } }
断路器代码段 2:使用该 CircuitBreakerBean。
@Inject CircuitBreakerBean bean; // FaultTolerance bean with circuit breaker, should fail 3 times for (int i = 0; i < 3; i++) { try { bean.serviceA(); throw new AssertionError("TimeoutException not caught"); } catch (TimeoutException e) { //expected } } // The CircuitBreaker should be open, so calling serviceA should generate a // CircuitBreakerOpenException. try { bean.serviceA(); throw new AssertionError("CircuitBreakerOpenException not caught"); } catch (CircuitBreakerOpenException e) { //expected } //allow time for the circuit to re-close Thread.sleep(3000); // The CircuitBreaker should be closed and serviceA should now succeed. String res = bean.serviceA(); if (!"serviceA: 4".equals(res)) { throw new AssertionError("Bad Result: " + res); }
回退和重试代码段 1:具有已配置的回退处理程序和重试策略的 FTServiceBean。
@RequestScoped public class FTServiceBean { // Annotate serviceA with a named FallbackHandler and a Retry policy specifying the // number of retries. @Retry(maxRetries = 2) @Fallback(StringFallbackHandler.class) public String serviceA() { throw new RuntimeException("Connection failed"); return null; } }
回退和重试代码段 2:在主服务失败的情况下驱动的回退处理程序代码。
@Dependent public class StringFallbackHandler implements FallbackHandler<String> { @Override public String handle(ExecutionContext context) { return "fallback for " + context.getMethod().getName(); } }
回退和重试代码段 3:使用该 FTServiceBean。
private @Inject FTServiceBean ftServiceBean; try { // Call serviceA, which will be retried twice in the event of failure, after which // the FallbackHandler will be driven. String result = ftServiceBean.serviceA(); if(!result.contains("serviceA")) throw new AssertionError("The message should be \"fallback for serviceA\""); } catch(RuntimeException ex) { throw new AssertionError("serviceA should not throw a RuntimeException"); }
隔板代码段 1:创建具有已配置的隔板的 BulkheadBean。
@RequestScoped @Asynchronous public class BulkheadBean { private final AtomicInteger connectATokens = new AtomicInteger(0); // Configure a Bulkhead that supports at most 2 concurrent threads. @Bulkhead(maxThreads = 2) public Future<Boolean> connectA(String data) throws InterruptedException { System.out.println("connectA starting " + data); int token = connectATokens.incrementAndGet(); try { if (token > 2) { throw new RuntimeException("Too many threads in connectA[" + data + "]: " + token); } Thread.sleep(5000); return CompletableFuture.completedFuture(Boolean.TRUE); } finally { connectATokens.decrementAndGet(); System.out.println("connectA complete " + data); } } }
隔板代码段 2:使用该 BulkheadBean。
@Inject BulkheadBean bean; // connectA has a poolSize of 2 // The first two calls to connectA should be run straight away, in parallel, each around // 5 seconds Future<Boolean> future1 = bean.connectA("One"); Thread.sleep(100); Future<Boolean> future2 = bean.connectA("Two"); Thread.sleep(100); // The next two calls to connectA should wait until the first 2 have finished Future<Boolean> future3 = bean.connectA("Three"); Thread.sleep(100); Future<Boolean> future4 = bean.connectA("Four"); Thread.sleep(100); //total time should be just over 10s Thread.sleep(11000); if (!future1.get(1000, TimeUnit.MILLISECONDS)) { throw new AssertionError("Future1 did not complete properly"); } if (!future2.get(1000, TimeUnit.MILLISECONDS)) { throw new AssertionError("Future2 did not complete properly"); } if (!future3.get(1000, TimeUnit.MILLISECONDS)) { throw new AssertionError("Future3 did not complete properly"); } if (!future4.get(1000, TimeUnit.MILLISECONDS)) { throw new AssertionError("Future4 did not complete properly"); }
父主题: 调整 Liberty

文件名:twlp_microprofile_fault_tolerance.html