Polly 重试并不总是捕获 HttpRequestException

Question

我的 .NET Core 3.1 应用程序使用 Polly 7.1.0 重试和舱壁策略来实现 http 弹性。重试策略使用

HandleTransientHttpError()

来捕获可能的

HttpRequestException

。

现在使用

MyClient

触发的 http 请求有时会返回

HttpRequestException

。其中大约一半被波莉抓住并重审。然而，另一半最终出现在我的

try-catch

块中，我必须手动重试它们。这种情况发生在最大重试次数用尽之前。

我如何设法创建一个竞争条件以防止 Polly 捕获所有异常？我该如何解决这个问题？

我使用

IHttpClientFactory

注册政策，如下。

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpClient<MyClient>(c =>
    {
        c.BaseAddress = new Uri("https://my.base.url.com/");
        c.Timeout = TimeSpan.FromHours(5); // Generous timeout to accomodate for retries
    })
        .AddPolicyHandler(GetHttpResiliencePolicy());
}

private static AsyncPolicyWrap<HttpResponseMessage> GetHttpResiliencePolicy()
{
    var delay = Backoff.DecorrelatedJitterBackoffV2(medianFirstRetryDelay: TimeSpan.FromSeconds(1), retryCount: 5);

    var retryPolicy = HttpPolicyExtensions
            .HandleTransientHttpError() // This should catch HttpRequestException
            .OrResult(msg => msg.StatusCode == HttpStatusCode.NotFound)
            .WaitAndRetryAsync(
                sleepDurations: delay,
                onRetry: (response, delay, retryCount, context) => LogRetry(response, retryCount, context));

    var throttlePolicy = Policy.BulkheadAsync<HttpResponseMessage>(maxParallelization: 50, maxQueuingActions: int.MaxValue);

    return Policy.WrapAsync(retryPolicy, throttlePolicy);
}

正在触发 http 请求的

MyClient

 如下所示。

public async Task<TOut> PostAsync<TOut>(Uri requestUri, string jsonString)
{
    try
    {
        using (var content = new StringContent(jsonString, Encoding.UTF8, "application/json"))
        using (var response = await httpClient.PostAsync(requestUri, content)) // This throws HttpRequestException
        {
            // Handle response
        }
    }
    catch (HttpRequestException ex)
    {
        // This should never be hit, but unfortunately is
    }
}

这里有一些附加信息，尽管我不确定它是否相关。

HttpClient
```
 是 
```
DI 暂时注册的，因此每个工作单元有 10 个它的实例。

Answer 1

重试，然后

HttpRequestException

每当我们谈论 Polly 政策时，我们都可以区分两种不同的例外情况：

处理异常

HttpRequestException
```
）。
```

未处理的异常

WebException
```
）。
```

“大约一半的人被波莉抓住并重审。
然而，另一半最终出现在我的 try-catch-block 中”

如果您的某些重试次数用完，则可能会发生这种情况。换句话说，有些请求在 6 次尝试（5 次重试和 1 次初始尝试）中无法成功。

这可以使用以下两个工具之一轻松验证：

onRetry
```
 + 
```
context
Fallback
```
 + 
```
context

onRetry

context

当重试策略被触发但在睡眠持续时间之前，会调用

onRetry

。代表收到

retryCount

。因此，为了能够连接/关联同一请求的单独日志条目，您需要使用某种相关 ID。最简单的方法可以像这样编码：

public static class ContextExtensions
{
    private const string Key = "CorrelationId";

    public static Context SetCorrelation(this Context context, Guid? id = null)
    {
        context[Key] = id ?? Guid.NewGuid();
        return context;
    }

    public static Guid? GetCorrelation(this Context context)
    {
        if (!context.TryGetValue(Key, out var id))
            return null;

        if (id is Guid correlation)
            return correlation;

        return null;
    }
}

这是一个简化的示例：

待执行的方法

private async Task<string> Test() 
{ 
    await Task.Delay(1000); 
    throw new CustomException(""); 
}

政策

var retryPolicy = Policy<string>
    .Handle<CustomException>()
    .WaitAndRetryAsync(5, _ => TimeSpan.FromSeconds(1),
        (result, delay, retryCount, context) =>
        {
            var id = context.GetCorrelation();
            Console.WriteLine($"{id} - #{retryCount} retry.");
        });

使用方法

var context = new Context().SetCorrelation();
try
{
    await retryPolicy.ExecuteAsync(async (ctx) => await Test(), context);
}
catch (CustomException)
{
    Console.WriteLine($"{context.GetCorrelation()} - All retry has been failed.");
}

示例输出

3319cf18-5e31-40e0-8faf-1fba0517f80d - #1 retry.
3319cf18-5e31-40e0-8faf-1fba0517f80d - #2 retry.
3319cf18-5e31-40e0-8faf-1fba0517f80d - #3 retry.
3319cf18-5e31-40e0-8faf-1fba0517f80d - #4 retry.
3319cf18-5e31-40e0-8faf-1fba0517f80d - #5 retry.
3319cf18-5e31-40e0-8faf-1fba0517f80d - All retry has been failed.

Fallback

正如所说，每当策略无法成功时，它将重新抛出已处理的异常。换句话说，如果一项政策失败，那么它会将问题升级到下一个级别（下一个外部政策）。

这是一个简化的示例：

政策

var fallbackPolicy = Policy<string>
    .Handle<CustomException>()
    .FallbackAsync(async (result, ctx, ct) =>
    {
        await Task.FromException<CustomException>(result.Exception);
        return result.Result; //it will never be executed << just to compile
    }, 
    (result, ctx) =>
    {
        Console.WriteLine($"{ctx.GetCorrelation()} - All retry has been failed.");
        return Task.CompletedTask;
    });

使用方法

var context = new Context().SetCorrelation();
try
{
    var strategy = Policy.WrapAsync(fallbackPolicy, retryPolicy);  
    await strategy.ExecuteAsync(async (ctx) => await Test(), context);
}
catch (CustomException)
{
    Console.WriteLine($"{context.GetCorrelation()} - All policies failed.");
}

示例输出

169a270e-acf7-45fd-8036-9bd1c034c5d6 - #1 retry.
169a270e-acf7-45fd-8036-9bd1c034c5d6 - #2 retry.
169a270e-acf7-45fd-8036-9bd1c034c5d6 - #3 retry.
169a270e-acf7-45fd-8036-9bd1c034c5d6 - #4 retry.
169a270e-acf7-45fd-8036-9bd1c034c5d6 - #5 retry.
169a270e-acf7-45fd-8036-9bd1c034c5d6 - All retry has been failed.
169a270e-acf7-45fd-8036-9bd1c034c5d6 - All policies failed.

Answer 2

我在使用 Polly 进行简单的 TCP 连接时遇到了同样的问题。

    // Manage connection errors
    this.reconnectPolicy = Policy
    .Handle<SocketException>()
    .Or<IOException>() // TODO - IOException is not been catch and throws 502 Bad Gateway Exception.
  .WaitAndRetryAsync(connectAttempts,
  (retryAttempt) => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)),
  (exception, timeSpan, retryCount, context) =>
  {
    var log = Log.ForContext("correlationId", context.CorrelationId);
    log.Warning(exception, "Lost connection to {serverName}. Retry {reconnectAttempt} in {reconnectWaitSeconds} seconds.", context["serverName"], retryCount, timeSpan.TotalSeconds);
  });

重启 TCP 监听服务后，第一个请求总是失败，后续请求成功。

        // Use a policy to auto-reconnect the connection
        var contextData = new Dictionary<string, object>()
        {
            ["serverName"] = serverName
        };
        var policyResult = await this.reconnectPolicy.ExecuteAndCaptureAsync(
            async (context, innerCancellationToken) =>
            {
                // Use existing TCP connection if possible, otherwise make a new connection
                var networkStream = connection.GetTcpClient(false).GetStream();

                await networkStream.WriteAsync(data, 0, data.Length, innerCancellationToken);

                return networkStream;
            },
            contextData,
            cancellationToken);

        // Interpret the policy result
        if (policyResult.Outcome == OutcomeType.Successful)
        {
            return policyResult.Result;
        }
        else
        {
            throw policyResult.FinalException ?? new Exception($"Unhandled fault connecting to {serverName}: {policyResult.FaultType}.");
        }

堆栈跟踪：

    Error Message [Unable to read data from the transport connection: An established connection was aborted by the software in your host machine.] There was a problem sending the HL7 message to the remote server.
System.IO.IOException: Unable to read data from the transport connection: An established connection was aborted by the software in your host machine. ---> System.Net.Sockets.SocketException: An established connection was aborted by the software in your host machine
   at System.Net.Sockets.Socket.BeginReceive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, AsyncCallback callback, Object state)
   at System.Net.Sockets.NetworkStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   --- End of inner exception stack trace ---
   at System.Net.Sockets.NetworkStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   at System.IO.Stream.<>c.<BeginEndReadAsync>b__43_0(Stream stream, ReadWriteParameters args, AsyncCallback callback, Object state)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncTrim[TInstance,TArgs](TInstance thisRef, TArgs args, Func`5 beginMethod, Func`3 endMethod)
   at System.IO.Stream.BeginEndReadAsync(Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.Stream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)

Polly 重试并不总是捕获 HttpRequestException

问题描述投票：0回答：2

2个回答

`HttpRequestException`

`onRetry`
+
`context`

`Fallback`

最新问题

Polly 重试并不总是捕获 HttpRequestException

问题描述 投票：0回答：2

2个回答

HttpRequestException

onRetry + context

Fallback

最新问题

问题描述投票：0回答：2

`HttpRequestException`

`onRetry`
+
`context`

`Fallback`