Polly断路器策略和使用ASP.NET核心API的HttpClient

Question

我在结合HttpClient设置Polly的断路器时遇到了问题。

具体来说，CircuitBreaker和HttpClient用于ASP.NET Core Web API Controller，其链接如下：

>

重试策略：如果出现暂时错误，则对每个请求重试3次。

cicuit断路器策略：如果所有请求中出现五个瞬态错误，则生效。

问题所在

配置Polly重试策略和断路器策略，并对自定义HttpClient，HttpClientService

    public void ConfigureServices(IServiceCollection services)
        {
           services.AddHttpClient();
           services.AddHttpClient<IHttpClientService, HttpClientService>()                                
                        .AddPolicyHandler((service, request) =>
                            HttpPolicyExtensions.HandleTransientHttpError()
                                .WaitAndRetryAsync(3,
                                    retryCount => TimeSpan.FromSeconds(Math.Pow(2, retryCount)),
                onRetry: (outcome, timespan, retryCount, context) =>
                                {
                                    service.GetService<ILog>().Error("Delaying for {delay}ms, then making retry {retry}.",
                                        timespan.TotalMilliseconds, retryCount);
                                }
                            )
)
                        )
                       .AddPolicyHandler((service, request) =>                      
                                HttpPolicyExtensions.HandleTransientHttpError()
                                    //Further external requests are blocked for 30 seconds if five failed attempts occur sequentially.
                                    //Circuit breaker policies are stateful.All calls through this client share the same circuit state.
                                    .CircuitBreakerAsync(5,
                                                 TimeSpan.FromSeconds(30), 
                                                 (result, timeSpan, context)=>
                                                            service.GetService<ILog>().Error("CircuitBreaker onBreak for {delay}ms", timeSpan.TotalMilliseconds),
                                                  context =>
                                                      service.GetService<ILog>().Error("CircuitBreaker onReset")));

         }

CarController

IHttpClientService是在ConfiguReservices的Polly策略中指定的。HttpClientService使用HttpClient。

 [ApiVersion("1")]
    [Route("api/v{version:apiVersion}/[controller]")]
    [ApiController]
    public class CarController : ControllerBase
    {
        private readonly ILog _logger;
        private readonly IHttpClientService _httpClientService;
        private readonly IOptions<Config> _config;

        public CarController(ILog logger, IHttpClientService httpClientService, IOptions<Config> config)
        {
            _logger = logger;
            _httpClientService = httpClientService;
            _config = config;
        }

        [HttpPost]
        public async Task<ActionResult> Post()
        {  

            using (StreamReader reader = new StreamReader(Request.Body, Encoding.UTF8))
            {
                string body = reader.ReadToEnd();

                    var statusCode = await _httpClientService.PostAsync(
                        "url",
                        new Dictionary<string, string>
                        {
                            {"headerID", "Id"}                           
                        },
                        body);
                    return StatusCode((int)statusCode);               
            }
        }
      }

 public class HttpClientService
{
    private readonly HttpClient _httpClient;
    public HttpClientService(HttpClient client)
    {
        _httpClient = client;
    }

    public async Task<HttpStatusCode> PostAsync(string url, Dictionary<string, string> headers, string body)
    {
        using (var content = new StringContent(body, Encoding.UTF8, "application/json"))
        {
            foreach (var keyValue in headers)
            {
                content.Headers.Add(keyValue.Key, keyValue.Value);
            }

             var request = new HttpRequestMessage(HttpMethod.Post, url)
                                    {
                                        Content = content
                                    };

            var response = await _httpClient.SendAsync(request);

            response.EnsureSuccessStatusCode();
            return response.StatusCode;
        }

    }

ASP.NET核心API 2.2

更新已更新的SetWaitAndRetryPolicy扩展方法以使用IServiceProvider。

Answer 1

断路器策略是有状态的，可以跟踪各个调用的故障率，因此需要长期使用，而不是根据每个请求创建。

所发布代码中HttpClientFactory上重载的使用方式：

.AddPolicyHandler((service, request) => HttpPolicyExtensions.HandleTransientHttpError()
    .CircuitBreakerAsync( /* etc */

是制造一个实例的断路器每一个请求，所以断路器从来没有时间建立一个故障状态。

.AddPolicyHandler(HttpPolicyExtensions.HandleTransientHttpError()
    .WaitAndRetryAsync(/* etc */))
.AddPolicyHandler(HttpPolicyExtensions.HandleTransientHttpError()
    .CircuitBreakerAsync(/* etc */))

var circuitBreaker = HttpPolicyExtensions.HandleTransientHttpError().CircuitBreakerAsync(/* etc */);
services.AddHttpClient<IHttpClientService, HttpClientService>()                                
    .AddPolicyHandler((service, request) => circuitBreaker); // By way of example technique: more typically with this overload, there is some more complex logic to select different policies for different kinds of request.

编辑以回答注释中的问题：该实例不必声明static以使其长期存在。它可以在startup.configureservices(...)方法中声明，就在使用之前，如上面的代码示例所示。lambda并在HttpClientFactory上配置它将捕获它并使其长期存在。

circuitbreaker实例应该在您想要中断的调用之间共享。如果将断路器附加到通过HttpClientFactory声明的特定HttpClient配置，则所有通过该HttpClient配置实例的调用都将共享该断路器，从而共享中断。

当将断路器与HttpClientFactory一起使用时，这通常意味着您可以在每个子系统上声明一个HttpClient配置（键入或命名），您希望对其进行断路器调用。

旁注：所选断路器的变种也根据连续故障计数触发。（这里提到的只是一个额外的因素；发布的问题提到了跨请求发生的5个错误，但不是具体连续发生的。）