Azure Service Bus连接异常时MassTransit重试策略未按配置生效求助

问题描述 #

创建了一个使用MassTransit对接Azure Service Bus的控制台应用，配置代码如下：

using System;
using System.Threading.Tasks;
using GreenPipes;
using MassTransit;
using Microsoft.Extensions.Azure;

namespace MassTransitRetryExample
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var busControl = Bus.Factory.CreateUsingAzureServiceBus(cfg =>
            {
                cfg.Host("My Service Bus Connection string");
                cfg.UseRetry(retryConfig =>
                {
                     retryConfig.Exponential(6, TimeSpan.FromSeconds(10), TimeSpan.FromSeconds(30), TimeSpan.FromSeconds(5));
                });

                cfg.ReceiveEndpoint("testqueue", ep =>
                {
                    ep.Consumer<YourMessageConsumer>();
                });
            });

            await busControl.StartAsync();

            Console.WriteLine("Sending a message...");
            await busControl.Publish(new YourMessage { Text = "Hello, World!" });

            Console.WriteLine("Press any key to stop receiving messages.");
            Console.ReadKey();

            await busControl.StopAsync();
        }
    }

当使用错误的Service Bus连接字符串导致连接失败时，系统抛出异常且仅重试4次，而非配置的6次，异常信息如下：

System.AggregateException: Retry failed after 4 tries. Retry settings can be adjusted in ClientOptions.Retry. (No such host is known. (my-bus.servicebus.windows.net:443)) (No such host is known. (my-bus.servicebus.windows.net:443)) (No such host is known. (my-bus.servicebus.windows.net:443)) (No such host is known. (my-bus.servicebus.windows.net:443))

Azure.RequestFailedException: No such host is known. (my-bus.servicebus.windows.net:443)

System.Net.Http.HttpRequestException: No such host is known. (my-bus.servicebus.windows.net:443)

System.Net.Sockets.SocketException (11001): No such host is known.

at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.System.Threading.Tasks.Sources.IValueTaskSource.GetResult(Int16 token)
at System.Net.Sockets.Socket.g__WaitForConnectWithCancellation|277_0(AwaitableSocketAsyncEventArgs saea, ValueTask connectTask, CancellationToken cancellationToken)
at System.Net.Http.HttpConnectionPool.ConnectToTcpHostAsync(String host, Int32 port, HttpRequestMessage initialRequest, Boolean async, CancellationToken cancellationToken)

使用版本：MassTransit 7.3.0、MassTransit.Azure.ServiceBus.Core 7.3.0。

原因分析 #

1. cfg.UseRetry的作用范围不覆盖连接阶段：你配置的cfg.UseRetry是针对消息消费阶段的异常重试，仅在消费者处理消息抛出异常时生效，完全不涉及总线与Azure Service Bus建立连接阶段的错误。
2. 4次重试来自Azure Service Bus客户端SDK默认策略：连接失败属于Azure Service Bus客户端SDK层面的错误，这部分的重试由SDK自带的默认策略控制，默认重试次数为4次，因此会看到4次重试后抛出异常。

解决方法 #

要调整连接阶段的重试策略，需要在cfg.Host的配置中单独设置Azure Service Bus客户端的重试规则，而非使用全局的UseRetry。修改后的代码如下：

var busControl = Bus.Factory.CreateUsingAzureServiceBus(cfg =>
{
    cfg.Host("My Service Bus Connection string", h =>
    {
        // 配置连接阶段的重试策略
        h.Retry(r =>
        {
            r.Exponential(6, TimeSpan.FromSeconds(10), TimeSpan.FromSeconds(30), TimeSpan.FromSeconds(5));
        });
    });

    // 此配置仅针对消息消费阶段的异常重试，与连接错误无关
    cfg.UseRetry(retryConfig =>
    {
         retryConfig.Exponential(6, TimeSpan.FromSeconds(10), TimeSpan.FromSeconds(30), TimeSpan.FromSeconds(5));
    });

    cfg.ReceiveEndpoint("testqueue", ep =>
    {
        ep.Consumer<YourMessageConsumer>();
    });
});

配置后，连接阶段的重试次数会按照设置的6次执行，消费阶段的重试依然由cfg.UseRetry控制。

内容的提问来源于stack exchange，提问作者Manoj Bang