Spring Cloud Gateway重试 Spring Cloud Gateway重试机制的实现

时间:2021-03-30 猿天地人气:0

前言

重试，我相信大家并不陌生。在我们调用Http接口的时候，总会因为某种原因调用失败，这个时候我们可以通过重试的方式，来重新请求接口。

生活中这样的事例很多，比如打电话，对方正在通话中啊，信号不好啊等等原因，你总会打不通，当你第一次没打通之后，你会打第二次，第三次...第四次就通了。

重试也要注意应用场景，读数据的接口比较适合重试的场景，写数据的接口就需要注意接口的幂等性了。还有就是重试次数如果太多的话会导致请求量加倍，给后端造成更大的压力，设置合理的重试机制才是最关键的。

今天我们来简单的了解下Spring Cloud Gateway中的重试机制和使用。

使用讲解

RetryGatewayFilter是Spring Cloud Gateway对请求重试提供的一个GatewayFilter Factory。

配置方式：

spring:
 cloud:
  gateway:
   routes:
   - id: fsh-house
    uri: lb://fsh-house
    predicates:
    - Path=/house/**
    filters:
    - name: Retry
     args:
      retries: 3
      series:
      - SERVER_ERROR
      statuses:
      - OK
      methods:
      - GET
      - POST
      exceptions:
      - java.io.IOException

配置讲解

配置类源码org.springframework.cloud.gateway.filter.factory.RetryGatewayFilterFactory.RetryConfig：

public static class RetryConfig {
  private int retries = 3;
    
  private List<Series> series = toList(Series.SERVER_ERROR);
    
  private List<HttpStatus> statuses = new ArrayList<>();
    
  private List<HttpMethod> methods = toList(HttpMethod.GET);

  private List<Class<? extends Throwable>> exceptions = toList(IOException.class);
    
  // .....
}

retries：重试次数，默认值是3次

series：状态码配置（分段），符合的某段状态码才会进行重试逻辑，默认值是SERVER_ERROR，值是5，也就是5XX(5开头的状态码)，共有5个值：

public enum Series {
  INFORMATIONAL(1),
  SUCCESSFUL(2),
  REDIRECTION(3),
  CLIENT_ERROR(4),
  SERVER_ERROR(5);
}

statuses：状态码配置，和series不同的是这边是具体状态码的配置，取值请参考：org.springframework.http.HttpStatus

methods：指定哪些方法的请求需要进行重试逻辑，默认值是GET方法，取值如下：

public enum HttpMethod {
  GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE;
}

exceptions：指定哪些异常需要进行重试逻辑，默认值是java.io.IOException

代码测试

就写个接口，在接口中记录请求次数，然后抛出一个异常模拟500，通过网关访问这个接口，如果你配置了重试次数是3，那么接口中会输出4次结果才是对的，证明重试生效了。

AtomicInteger ac = new AtomicInteger();

@GetMapping("/data")
public HouseInfo getData(@RequestParam("name") String name) {
  if (StringUtils.isBlank(name)) {
    throw new RuntimeException("error");
  }
  System.err.println(ac.addAndGet(1));
  return new HouseInfo(1L, "上海", "虹口", "XX小区");
}

更多Spring Cloud代码尽在：https://github.com/yinjihuan/spring-cloud

源码欣赏

  @Override
  public GatewayFilter apply(RetryConfig retryConfig) {
    // 验证重试配置格式是否正确
    retryConfig.validate();

    Repeat<ServerWebExchange> statusCodeRepeat = null;
    if (!retryConfig.getStatuses().isEmpty() || !retryConfig.getSeries().isEmpty()) {
      Predicate<RepeatContext<ServerWebExchange>> repeatPredicate = context -> {
        ServerWebExchange exchange = context.applicationContext();
        // 判断重试次数是否已经达到了配置的最大值
        if (exceedsMaxIterations(exchange, retryConfig)) {
          return false;
        }
        // 获取响应的状态码
        HttpStatus statusCode = exchange.getResponse().getStatusCode();
        // 获取请求方法类型
        HttpMethod httpMethod = exchange.getRequest().getMethod();
        // 判断响应状态码是否在配置中存在
        boolean retryableStatusCode = retryConfig.getStatuses().contains(statusCode);

        if (!retryableStatusCode && statusCode != null) { // null status code might mean a network exception?
          // try the series
          retryableStatusCode = retryConfig.getSeries().stream()
              .anyMatch(series -> statusCode.series().equals(series));
        }
        // 判断方法是否包含在配置中
        boolean retryableMethod = retryConfig.getMethods().contains(httpMethod);
        // 决定是否要进行重试
        return retryableMethod && retryableStatusCode;
      };

      statusCodeRepeat = Repeat.onlyIf(repeatPredicate)
          .doOnRepeat(context -> reset(context.applicationContext()));
    }

    //TODO: support timeout, backoff, jitter, etc... in Builder

    Retry<ServerWebExchange> exceptionRetry = null;
    if (!retryConfig.getExceptions().isEmpty()) {
      Predicate<RetryContext<ServerWebExchange>> retryContextPredicate = context -> {
        if (exceedsMaxIterations(context.applicationContext(), retryConfig)) {
          return false;
        }
        // 异常判断
        for (Class<? extends Throwable> clazz : retryConfig.getExceptions()) {       
          if (clazz.isInstance(context.exception())) {
            return true;
          }
        }
        return false;
      };
      // 使用reactor extra的retry组件
      exceptionRetry = Retry.onlyIf(retryContextPredicate)
          .doOnRetry(context -> reset(context.applicationContext()))
          .retryMax(retryConfig.getRetries());
    }


    return apply(statusCodeRepeat, exceptionRetry);
  }

  public boolean exceedsMaxIterations(ServerWebExchange exchange, RetryConfig retryConfig) {
    Integer iteration = exchange.getAttribute(RETRY_ITERATION_KEY);

    //TODO: deal with null iteration
    return iteration != null && iteration >= retryConfig.getRetries();
  }

  public void reset(ServerWebExchange exchange) {
    //TODO: what else to do to reset SWE?
    exchange.getAttributes().remove(ServerWebExchangeUtils.GATEWAY_ALREADY_ROUTED_ATTR);
  }

  public GatewayFilter apply(Repeat<ServerWebExchange> repeat, Retry<ServerWebExchange> retry) {
    return (exchange, chain) -> {
      if (log.isTraceEnabled()) {
        log.trace("Entering retry-filter");
      }

      // chain.filter returns a Mono<Void>
      Publisher<Void> publisher = chain.filter(exchange)
          //.log("retry-filter", Level.INFO)
          .doOnSuccessOrError((aVoid, throwable) -> {
            // 获取已经重试的次数，默认值为-1
            int iteration = exchange.getAttributeOrDefault(RETRY_ITERATION_KEY, -1);
            // 增加重试次数
            exchange.getAttributes().put(RETRY_ITERATION_KEY, iteration + 1);
          });

      if (retry != null) {
        // retryWhen returns a Mono<Void>
        // retry needs to go before repeat
        publisher = ((Mono<Void>)publisher).retryWhen(retry.withApplicationContext(exchange));
      }
      if (repeat != null) {
        // repeatWhen returns a Flux<Void>
        // so this needs to be last and the variable a Publisher<Void>
        publisher = ((Mono<Void>)publisher).repeatWhen(repeat.withApplicationContext(exchange));
      }

      return Mono.fromDirect(publisher);
    };
  }

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