Polly 和多个 HttpClients

Question

我想将 Polly 与我的 HttpClientFactory 结合使用（在我的 C# .NET 5.0 项目中）。

但我遇到的问题是我的工厂中有多个命名的 HttpClients，而我想要实现的是当我有一个特定的状态代码时，例如404 我想使用我工厂的 另一个名为 HttpClient 的 重试（指向不同的服务器）。

但我看到人们经常使用 services.AddHttpClient(name, configureOptions).AddPolicyHandler() 模式。但那是行不通的，因为那不会调用另一个命名的 HttpClient。

我还想在 408 发生时“为他们自己”重试两个客户端。

是否有任何模式或示例代码？我不知道最好的前进方向是什么。

Answer 1

我认为您可以通过以下方式实现所需的行为。

让我们注册两个命名的 http 客户端，在出现 408 状态代码时重试：

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpClient("ServiceA")
        .AddPolicyHandler(GetRetryPolicy("ServiceA"));

    services.AddHttpClient("ServiceB")
        .AddPolicyHandler(GetRetryPolicy("ServiceB"));

    //...
}

private IAsyncPolicy<HttpResponseMessage> GetRetryPolicy(string name)
    => Policy<HttpResponseMessage>
    .HandleResult(res => res.StatusCode == System.Net.HttpStatusCode.RequestTimeout)
    .WaitAndRetryAsync(3, _ => TimeSpan.FromMilliseconds(200),
    onRetryAsync: (dr, ts) => { Console.WriteLine($"Retry by {name}"); return Task.CompletedTask; });

我提供了一个 onRetryAsync 用于调试目的，只是为了查看重试何时执行。

现在让我们用一个简单的 webapi 控制器来连接东西：

[Route("api/[controller]")]
public class HomeController : Controller
{
    private readonly IHttpClientFactory clientFactory;
    public HomeController(IHttpClientFactory clientFactory)
    {
        this.clientFactory = clientFactory;
    }

    [HttpGet]
    public async Task<IActionResult> Get(int expectedStatusCode)
    {
        var result = await GetAsync(GetPrimaryProxy(), expectedStatusCode);
        if(result != null && result.StatusCode == System.Net.HttpStatusCode.NotFound)
            result = await GetAsync(GetSecondaryProxy(), expectedStatusCode);

        return StatusCode(500, result);
    }

    private HttpClient GetPrimaryProxy() => clientFactory.CreateClient("ServiceA");
    private HttpClient GetSecondaryProxy() => clientFactory.CreateClient("ServiceB");

    private async Task<HttpResponseMessage> GetAsync(HttpClient client, int expectedStatusCode)
        => await client.GetAsync($"https://httpstat.us/{expectedStatusCode}");
}

我已经使用 https://httpstat.us 网站来模拟预期的响应状态代码
很遗憾，您必须手动进行故障转移。无法以检查 HttpResponseMessage 和 returns 和 HttpClient.

`/api/Home/404`

调试日志：

System.Net.Http.HttpClient.ServiceA.LogicalHandler: Information: Start processing HTTP request GET https://httpstat.us/404
info: System.Net.Http.HttpClient.ServiceA.LogicalHandler[100]
      Start processing HTTP request GET https://httpstat.us/404
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[100]
      Sending HTTP request GET https://httpstat.us/404
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Sending HTTP request GET https://httpstat.us/404
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[101]
      Received HTTP response headers after 319.9439ms - 404
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Received HTTP response headers after 319.9439ms - 404
info: System.Net.Http.HttpClient.ServiceA.LogicalHandler[101]
      End processing HTTP request after 326.1409ms - 404
System.Net.Http.HttpClient.ServiceA.LogicalHandler: Information: End processing HTTP request after 326.1409ms - 404

info: System.Net.Http.HttpClient.ServiceB.LogicalHandler[100]
      Start processing HTTP request GET https://httpstat.us/404
System.Net.Http.HttpClient.ServiceB.LogicalHandler: Information: Start processing HTTP request GET https://httpstat.us/404
info: System.Net.Http.HttpClient.ServiceB.ClientHandler[100]
      Sending HTTP request GET https://httpstat.us/404
System.Net.Http.HttpClient.ServiceB.ClientHandler: Information: Sending HTTP request GET https://httpstat.us/404
info: System.Net.Http.HttpClient.ServiceB.ClientHandler[101]
      Received HTTP response headers after 344.5937ms - 404
System.Net.Http.HttpClient.ServiceB.ClientHandler: Information: Received HTTP response headers after 344.5937ms - 404
info: System.Net.Http.HttpClient.ServiceB.LogicalHandler[101]
      End processing HTTP request after 350.932ms - 404
System.Net.Http.HttpClient.ServiceB.LogicalHandler: Information: End processing HTTP request after 350.932ms - 404

ServiceA发出请求，收到404
- Retry 未触发，因为仅处理 408
ServiceB发出请求，收到404
- Retry 未触发，因为仅处理 408

`/api/Home/408`

调试日志：

info: System.Net.Http.HttpClient.ServiceA.LogicalHandler[100]
      Start processing HTTP request GET https://httpstat.us/408
System.Net.Http.HttpClient.ServiceA.LogicalHandler: Information: Start processing HTTP request GET https://httpstat.us/408
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[100]
      Sending HTTP request GET https://httpstat.us/408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Sending HTTP request GET https://httpstat.us/408
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[101]
      Received HTTP response headers after 343.5167ms - 408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Received HTTP response headers after 343.5167ms - 408

Retry by ServiceA
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[100]
      Sending HTTP request GET https://httpstat.us/408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Sending HTTP request GET https://httpstat.us/408
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[101]
      Received HTTP response headers after 236.9796ms - 408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Received HTTP response headers after 236.9796ms - 408

Retry by ServiceA
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[100]
      Sending HTTP request GET https://httpstat.us/408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Sending HTTP request GET https://httpstat.us/408
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[101]
      Received HTTP response headers after 207.2602ms - 408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Received HTTP response headers after 207.2602ms - 408

Retry by ServiceA
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[100]
      Sending HTTP request GET https://httpstat.us/408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Sending HTTP request GET https://httpstat.us/408
info: System.Net.Http.HttpClient.ServiceA.ClientHandler[101]
      Received HTTP response headers after 203.3911ms - 408
System.Net.Http.HttpClient.ServiceA.ClientHandler: Information: Received HTTP response headers after 203.3911ms - 408
System.Net.Http.HttpClient.ServiceA.LogicalHandler: Information: End processing HTTP request after 1618.0826ms - 408
info: System.Net.Http.HttpClient.ServiceA.LogicalHandler[101]
      End processing HTTP request after 1618.0826ms - 408

ServiceA发出请求，收到408
- Retry 在 200 毫秒延迟后触发
ServiceA发出请求，收到408
- Retry 在 200 毫秒延迟后触发
ServiceA发出请求，收到408
- Retry 在 200 毫秒延迟后触发
ServiceA发出请求，收到408
- Retry 未触发，因为超过了最大重试次数
ServiceB 未被调用，因为状态代码是 408 而不是 404

Answer 2

我最终没有使用 PollyHttpClientBuilderExtensions.AddPolicyHandler 但我用它作为灵感来编写我自己的：https://github.com/App-vNext/Polly-Samples/blob/master/PollyDemos/Async/AsyncDemo08_Wrap-Fallback-WaitAndRetry-CircuitBreaker.cs

Polly 和多个 HttpClients

Polly and Multiple HttpClients

c#

dotnet-httpclient

polly

`/api/Home/404`

`/api/Home/408`