CircuitBreaker 断路器
服务熔断是为了保护我们的服务，比如当某个服务出现问题的时候，控制打向它的流量，让它有时间去恢复，或者限制一段时间只能有固定数量的请求打向这个服务。这些都是保护措施。我在实际工作中也确实遇到过，数据库出现问题了，进而导致Web服务出现问题了，导致不依赖数据库的服务也出现问题了，出现一连串问题。 这次学习《玩转 Spring 全家桶》，丁雪丰老师给了使用resilience4j的例子。 丁老师的例子是2019年的，这个框架已经修改了些方法，所以我自己也花了些时间来理解了它的用法。现将过程记录下来。
首先POM文件引入
io.github.resilience4j resilience4j-spring-boot2 2.0.2
接着改造之前的Controller方法
@RestController
@RequestMapping("/customer")
@Slf4j
public class BookController {
@Autowired
private BookService bookService;
private CircuitBreaker circuitBreaker;
public BookController(CircuitBreakerRegistry registry) {
circuitBreaker = registry.circuitBreaker("menu");
}
@GetMapping("/menu")
public List readMenu() {
Supplier> supplier = () -> bookService.getAll();
circuitBreaker.getEventPublisher()
.onEvent(event -> log.info(event.toString()));
try{
return circuitBreaker.executeSupplier(supplier);
}
catch (Exception ex)
{
log.error(ex.getMessage());
return Collections.emptyList();
}
}
}
不同的地方就是引入了CircuitBreaker， 然后使用它将我们的方法“bookService.getAll()”包起来了。
然后在配置文件中添加如下的配置
resilience4j.circuitbreaker.backends.menu.failure-rate-threshold=50 resilience4j.circuitbreaker.backends.menu.wait-duration-in-open-state=60000 resilience4j.circuitbreaker.backends.menu.sliding-window-size=5 resilience4j.circuitbreaker.backends.menu.permitted-number-of-calls-in-half-open-state=2 resilience4j.circuitbreaker.backends.menu.minimum-number-of-calls=2
稍微解释一下这里的配置
failure-rate-threshold=50是说失败率超过50%就熔断，
wait-duration-in-open-state= 60000，是说熔断后等待60S才允许再次调用。
sliding-window-size =5 可以理解为5个请求统计一次，
permitted-number-of-calls-in-half-open-state = 2是说进入半开的状态的时候，还允许请求多少个。
minimum-number-of-calls=2是说最少有多少个请求才开始统计。 这里的参数都是我为了实验设置的，实际情况根据需要进行调整。参数比较多，具体可以参加官方文档
https://resilience4j.readme.io/docs/circuitbreaker
我们来看下实际的效果通过浏览器访问，
首先我们现打开BookService，让它有一次成功的请求，日志会输出
CircuitBreaker 'menu' recorded a successful call.
然后我们将BookService关闭，让它请求失败，日志会输出如下
CircuitBreaker 'menu' recorded an error: 'feign.RetryableException: Connection refused: no further information executing GET http://bookshop-service/book/getAll'. Elapsed time: 2050 ms
CircuitBreaker 'menu' exceeded failure rate threshold. Current failure rate: 50.0
CircuitBreaker 'menu' changed state from CLOSED to OPEN
可以看到断路器已经打开了，
接着我们继续访问会出现，
CircuitBreaker 'menu' recorded a call which was not permitted.
这个时候请求不会打到BookService上面了。就算这个时候我们的BookService恢复正常。
等待60s后进入半Open的状态
CircuitBreaker 'menu' changed state from OPEN to HALF_OPEN
这个时候恢复BookService正常，我们请求也会正常响应了
CircuitBreaker 'menu' recorded a successful call
多请求几次，断路器就从HALF_OPEN变成了CLOSED
CircuitBreaker 'menu' changed state from HALF_OPEN to CLOSED
这里给一个官方的状态图来说明
断路器有三个状态： CLOSED， OPEN， HALF_OPEN。
CLOSED是最开始的状态，也就是关闭状态，流量可以正常通过，当失败比率超过threshold后，断路器打开， 变成OPEN 打开后流量不可以通过；等待一定的时间后，断路器进入半开状态 HALF_OPEN, 这个时候如果失败率低于阈值，断路器进入CLOSED状态，如果超过阈值，断路器继续保证OPEN，再等待，如此往复。
断路器现在还支持设置慢请求，使用起来还是比较方便。对于参数的设置如果不是很理解，可以通过单元测试的方法来加深对它的理解。这里参考https://github.com/eugenp/tutorials/blob/master/libraries-6/src/test/java/com/baeldung/resilence4j/Resilience4jUnitTest.java 上面的例子，给出来个单元测试
interface RemoteService {
int process(int i);
}
private RemoteService service;
@Test
public void whenCircuitBreakerIsUsed_thenItWorksAsExpected() {
service = mock(RemoteService.class);
CircuitBreakerConfig config = CircuitBreakerConfig.custom()
// Percentage of failures to start short-circuit
.failureRateThreshold(20)
.minimumNumberOfCalls(5)
.build();
CircuitBreakerRegistry registry = CircuitBreakerRegistry.of(config);
CircuitBreaker circuitBreaker = registry.circuitBreaker("my");
Function decorated = CircuitBreaker.decorateFunction(circuitBreaker, service::process);
when(service.process(anyInt())).thenThrow(new RuntimeException());
circuitBreaker.getEventPublisher()
.onEvent(event ->
{
log.info(event.toString());
});
for (int i = 0; i < 10; i++) {
try {
decorated.apply(i);
} catch (Exception ignore) {
}
}
verify(service, times(5)).process(any(Integer.class));
}
这里设置最少请求5次，失败率超过20%就熔断，然后我们请求了10次，实际上只调用了Service5次。
对于其它参数，你可以调整后，根据需要来验证是否符合预期。它的日志输出如下
CircuitBreaker 'my' recorded an error: 'java.lang.RuntimeException'. Elapsed time: 2 ms
CircuitBreaker 'my' recorded an error: 'java.lang.RuntimeException'. Elapsed time: 0 ms
CircuitBreaker 'my' recorded an error: 'java.lang.RuntimeException'. Elapsed time: 0 ms
CircuitBreaker 'my' recorded an error: 'java.lang.RuntimeException'. Elapsed time: 0 ms
CircuitBreaker 'my' recorded an error: 'java.lang.RuntimeException'. Elapsed time: 0 ms
CircuitBreaker 'my' exceeded failure rate threshold. Current failure rate: 100.0
CircuitBreaker 'my' changed state from CLOSED to OPEN
CircuitBreaker 'my' recorded a call which was not permitted.
CircuitBreaker 'my' recorded a call which was not permitted.
CircuitBreaker 'my' recorded a call which was not permitted.
CircuitBreaker 'my' recorded a call which was not permitted.
CircuitBreaker 'my' recorded a call which was not permitted.
可以看到5次过后，就开始打开断路器，后面的call就不被允许了。
隔舱Bulkhead
Resilience4j 里面的Bulkhead可以简单的理解为允许多少个并发访问。我们这里还是通过单元测试的方法来演示它的功能
@Test
public void whenBulkheadIsUsed_thenItWorksAsExpected() throws InterruptedException {
service = mock(RemoteService.class);
BulkheadConfig config = BulkheadConfig.custom().maxConcurrentCalls(2).build();
BulkheadRegistry registry = BulkheadRegistry.of(config);
Bulkhead bulkhead = registry.bulkhead("my");
Function decorated = Bulkhead.decorateFunction(bulkhead, service::process);
try {
callAndBlock(decorated);
}
catch(BulkheadFullException ex)
{
log.error("isfull");
}
finally
{
verify(service, times(2)).process(any(Integer.class));
}
}
private void callAndBlock(Function decoratedService) throws InterruptedException {
when(service.process(anyInt())).thenAnswer(invocation -> {
log.info("service called");
return null;
});
ArrayList numberList = new ArrayList();
for(int i = 0;i<10;i++)
{
numberList.add(i);
}
numberList.parallelStream().forEach((i)->{
try {
decoratedService.apply(i);
}
catch (Exception ex)
{
log.error("meet error " + ex.getMessage());
} catch (Throwable e) {
throw new RuntimeException(e);
}
});
}
首先我们解读一下callAndBlock， 它会并发的去执行一个function. 如果我们不用隔舱，它的输出会是这样。
2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-4] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-9] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-5] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-3] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-1] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-6] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-7] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-8] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.010+08:00 INFO 37276 --- [onPool-worker-2] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:22:52.011+08:00 INFO 37276 --- [ main] c.k.r.bookcustomer.Resilience4jUnitTest : service called可以看到启动了10个线程去访问方法。加了隔舱后，隔舱限定了一次只能两个，输出如下
2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-4] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-6] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-7] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-4] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-8] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-5] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-2] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.648+08:00 ERROR 32256 --- [onPool-worker-3] c.k.r.bookcustomer.Resilience4jUnitTest : meet error Bulkhead 'my' is full and does not permit further calls2022-12-28T15:33:48.650+08:00 INFO 32256 --- [onPool-worker-1] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:33:48.650+08:00 INFO 32256 --- [ main] c.k.r.bookcustomer.Resilience4jUnitTest : service called可以看到只有两次成功的访问，其它的访问都被block了。
限速器RateLimiter
RateLimiter的功能是限定一段时间内允许多少次访问，还是使用和Bulkhead一样的例子一样
@Test public void whenRateLimiterInUse_thenItWorksAsExpected() throws InterruptedException { service = mock(RemoteService.class); RateLimiterConfig config = RateLimiterConfig.custom() .limitRefreshPeriod(Duration.ofMillis(1000)) .limitForPeriod(4) .timeoutDuration(Duration.ofMillis(25)) .build(); RateLimiterRegistry rateLimiterRegistry = RateLimiterRegistry.of(config); RateLimiter rateLimiter = rateLimiterRegistry .rateLimiter("name1"); CheckedFunction decorated = RateLimiter .decorateCheckedFunction(rateLimiter, service::process); try { callAndBlock(decorated); } catch(Exception ex) { log.error("isfull"); } finally { verify(service, times(4)).process(any(Integer.class)); } } private void callAndBlock(CheckedFunction decoratedService) throws InterruptedException { when(service.process(anyInt())).thenAnswer(invocation -> { log.info("service called"); return null; }); ArrayList numberList = new ArrayList(); for(int i = 0;i<10;i++) { numberList.add(i); } numberList.parallelStream().forEach((i)->{ try { decoratedService.apply(i); } catch (Exception ex) { log.error("meet error " + ex.getMessage()); } catch (Throwable e) { throw new RuntimeException(e); } }); } 我们这里故意设置1S中允许访问4次，实际的运行情况也是只允许了4次。日志输出如下
2022-12-28T15:39:52.027+08:00 INFO 35236 --- [onPool-worker-2] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:39:52.027+08:00 INFO 35236 --- [onPool-worker-5] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:39:52.027+08:00 INFO 35236 --- [ main] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:39:52.027+08:00 INFO 35236 --- [onPool-worker-7] c.k.r.bookcustomer.Resilience4jUnitTest : service called2022-12-28T15:39:52.053+08:00 ERROR 35236 --- [onPool-worker-6] c.k.r.bookcustomer.Resilience4jUnitTest : meet error RateLimiter 'name1' does not permit further calls2022-12-28T15:39:52.060+08:00 ERROR 35236 --- [onPool-worker-3] c.k.r.bookcustomer.Resilience4jUnitTest : meet error RateLimiter 'name1' does not permit further calls2022-12-28T15:39:52.060+08:00 ERROR 35236 --- [onPool-worker-9] c.k.r.bookcustomer.Resilience4jUnitTest : meet error RateLimiter 'name1' does not permit further calls2022-12-28T15:39:52.060+08:00 ERROR 35236 --- [onPool-worker-1] c.k.r.bookcustomer.Resilience4jUnitTest : meet error RateLimiter 'name1' does not permit further calls2022-12-28T15:39:52.060+08:00 ERROR 35236 --- [onPool-worker-8] c.k.r.bookcustomer.Resilience4jUnitTest : meet error RateLimiter 'name1' does not permit further calls2022-12-28T15:39:52.075+08:00 ERROR 35236 --- [onPool-worker-4] c.k.r.bookcustomer.Resilience4jUnitTest : meet error RateLimiter 'name1' does not permit further calls限速器这个功能只能限制在整体性能上面，如果要限制某个用户，只能某段时间访问多少次，它就做不到了。
Relilience4j 里面还提供了Retry,TimeLimiter,Cache. 感觉不是很有必要的功能， Retry在spring里面有相应的功能了，没有必要专门为了使用它而多加个包。 TimeLimiter，Cache 我感觉不是很受重视的功能，连例子文档都懒得提供，可见意义不大。