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改良 Liberty 中的微服務復原力
您可以使用「MicroProfile 容錯」特性,讓服務的呼叫更具復原力。這項特性是「Eclipse MicroProfile 容錯規格 1.0」的實作。此特性使用 Failsafe 開放程式碼庫來提供一個程式設計模型,以透過各種型樣來支援具復原力的微服務,這些型樣包括:重試、斷路器、隔板、逾時和備用。
開始之前
程序
- 將 mpFaultTolerance-1.0 特性新增至 server.xml 檔中的 featureManager 元素。
<featureManager> <feature>mpFaultTolerance-1.0</feature> </featureManager>
- 使用程式碼 Snippet,來改良微服務的復原力。 容錯斷路器提供一種作法,讓系統快點失敗。它會暫時讓服務無法執行,避免服務讓系統超載。容錯 RetryPolicy 提供一種用來配置何時重試服務的作法。如果主要服務失敗,容錯備用可以指定要使用的服務。「隔板」容錯用來限制對某服務的並行呼叫數。隔板會限制服務呼叫所能使用的系統資源量。程式碼 Snippet 會要求 server.xml 檔中除了指定 mpFaultTolerance-1.0 特性,還需指定 Liberty concurrent-1.0 特性。
「斷路器」程式碼 Snippet 1:建立配置了 CircuitBreaker 和 Timeout 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"); } }
CircuitBreaker 程式碼 Snippet 2:使用 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); }
「備用和重試」程式碼 Snippet 1:配置了 FallbackHandler 和 Retry 原則的 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; } }
「備用和重試」程式碼 Snippet 2:FallbackHandler,這是一旦主要服務失敗要驅動的程式碼
@Dependent public class StringFallbackHandler implements FallbackHandler<String> { @Override public String handle(ExecutionContext context) { return "fallback for " + context.getMethod().getName(); } }
「備用和重試」程式碼 Snippet 3:使用 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」程式碼 Snippet 1:建立配置了 Bulkhead 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」程式碼 Snippet 2:使用 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"); }
上層主題: 調整 Liberty

檔名:twlp_microprofile_fault_tolerance.html