Spring Cloud Gateway重试机制的实现

时间:2022-09-26 11:30:38

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:

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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:

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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:

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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:

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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。

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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

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@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);
  };
}

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。

原文链接:https://segmentfault.com/a/1190000018469096