关于Spring Cloud Gateway重试机制的简介
更新:HHH   时间:2023-1-7


小编给大家分享一下关于Spring Cloud Gateway重试机制的简介,相信大部分人都还不怎么了解,因此分享这篇文章给大家参考一下,希望大家阅读完这篇文章后大有收获,下面让我们一起去了解一下吧!

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<&#63; 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");
}

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&#63;
        // 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<&#63; 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&#63;
  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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