请求重试

请求重试

当一次服务调用失败时，我们可以让框架选择自动重试几次，这样能提高用户侧看到的请求成功率。在 failover cluster 模式下 dubbo-go 支持自动重试。

1.介绍

本示例演示如何在 client 端调用失败时配置重试功能，完整示例源码地址

2.如何使用重试功能

在使用 client.NewClient() 创建客户端时，可以使用 client.WithClientRetries() 方法设置重试次数。

cli, err := client.NewClient(
    client.WithClientURL("tri://127.0.0.1:20000"),
    client.WithClientRetries(3),
)

或者，可以使用 client.WithRequestTimeout() 设置服务粒度的超时时间（以下配置对服务 svc 起作用）。

svc, err := greet.NewGreetService(cli, client.WithClientRetries(5))

也可以在调用发起时，使用 client.WithCallRetries() 指定重试次数

resp, err := svc.Greet(context.Background(), &greet.GreetRequest{Name: "hello world"}, client.WithCallRetries(6))

从上往下，以上三种方式的优先级逐步提高，client.WithCallRetries() 指定的重试次数优先级最高。

3.示例解读

3.1服务端介绍

服务端proto文件

源文件路径：dubbo-go-sample/retry/proto/greet.proto

syntax = "proto3";
package greet;
option go_package = "github.com/apache/dubbo-go-samples/retry/proto;greet";
message GreetRequest {
  string name = 1;
}
message GreetResponse {
  string greeting = 1;
}
service GreetService {
  rpc Greet(GreetRequest) returns (GreetResponse) {}
  rpc GreetTimeout(GreetRequest) returns (GreetResponse) {}
}

服务端handler文件

Greet方法直接响应，GreetRetry方法用于模拟重试。

package main
import (
    "context"
    "github.com/pkg/errors"
    _ "dubbo.apache.org/dubbo-go/v3/imports"
    "dubbo.apache.org/dubbo-go/v3/protocol"
    "dubbo.apache.org/dubbo-go/v3/server"
    greet "github.com/apache/dubbo-go-samples/retry/proto"
    "github.com/dubbogo/gost/log/logger"
)
type GreetTripleServer struct {
    requestTime int
}
func (srv *GreetTripleServer) Greet(ctx context.Context, req *greet.GreetRequest) (*greet.GreetResponse, error) {
    resp := &greet.GreetResponse{Greeting: req.Name}
    logger.Info("Not need retry, request success")
    return resp, nil
}
func (srv *GreetTripleServer) GreetRetry(ctx context.Context, req *greet.GreetRequest) (*greet.GreetResponse, error) {
    if srv.requestTime < 3 {
        srv.requestTime++
        logger.Infof("retry %d times", srv.requestTime)
        return nil, errors.New("retry")
    }
    resp := &greet.GreetResponse{Greeting: req.Name}
    logger.Infof("retry success, current request time is %d", srv.requestTime)
    srv.requestTime = 0
    return resp, nil
}
func main() {
    srv, err := server.NewServer(
        server.WithServerProtocol(
            protocol.WithPort(20000),
        ),
    )
    if err != nil {
        panic(err)
    }
    if err := greet.RegisterGreetServiceHandler(srv, &GreetTripleServer{
        requestTime: 0,
    }); err != nil {
        panic(err)
    }
    if err := srv.Serve(); err != nil {
        logger.Error(err)
    }
}

3.2客户端介绍

客户端client文件，创建客户端，设置重试次数为3，分别请求Greet和GreetRetry，观察服务端日志输出。

package main
import (
    "context"
    "dubbo.apache.org/dubbo-go/v3/client"
    _ "dubbo.apache.org/dubbo-go/v3/imports"
    greet "github.com/apache/dubbo-go-samples/retry/proto"
    "github.com/dubbogo/gost/log/logger"
)
func main() {
    cli, err := client.NewClient(
        client.WithClientURL("tri://127.0.0.1:20000"),
        client.WithClientRetries(3),
    )
    if err != nil {
        panic(err)
    }
    svc, err := greet.NewGreetService(cli)
    if err != nil {
        panic(err)
    }
    // request normal
    resp, err := svc.Greet(context.Background(), &greet.GreetRequest{Name: "hello world"})
    if err != nil {
        logger.Error(err)
    }
    logger.Infof("Greet response: %s", resp.Greeting)
    // request need retry
    resp, err = svc.GreetRetry(context.Background(), &greet.GreetRequest{Name: "hello world"})
    if err != nil {
        logger.Error(err)
    }
    logger.Infof("Greet response: %s", resp.Greeting)
}

3.3案例效果

先启动服务端，再启动客户端，访问GreetRetry时观察到服务端日志输出了重试次数。

2024-01-23 22:39:11     INFO    logger/logging.go:22    [Not need retry, request success]
2024-01-23 22:39:11     INFO    logger/logging.go:42    retry [1] times
2024-01-23 22:39:11     INFO    logger/logging.go:42    retry [2] times
2024-01-23 22:39:11     INFO    logger/logging.go:42    retry [3] times
2024-01-23 22:39:11     INFO    logger/logging.go:42    retry success, current request time is [3]

最后修改 September 13, 2024: Refactor website structure (#2860) (1a4b998f54b)