HttpClientFactory + Polly 实现熔断降级

HttpClientFactory 是 ASP.NET CORE 2.1 中新增加的功能,目的是为了解决直接使用 HttpClient 可能带来的一系列问题(优雅通过 HttpClientFactory 使用 HttpClient),本文主要介绍 HttpClientFactory 整合 Polly 的使用,实现对 Http 请求的超时、重试、熔断、降级等操作。

HttpClientFactory 集成 Polly

  1. 创建 .NET Core API 项目(这里使用的是 .NET Core 2.2);

  2. 安装 Microsoft.Extensions.Http.Polly NuGet Package;

  3. 在 Startup.cs 的 ConfigureServices 方法中添加 HttpClient 相关代码:

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    public void ConfigureServices(IServiceCollection services)
    {
    var fallbackResponse = new HttpResponseMessage
    {
    Content = new StringContent("Fallback"),
    StatusCode = HttpStatusCode.GatewayTimeout
    };

    services.AddHttpClient("github", client =>
    {
    client.BaseAddress = new Uri("https://www.github.com");
    })
    // 降级
    .AddPolicyHandler(Policy<HttpResponseMessage>.Handle<Exception>().FallbackAsync(fallbackResponse, async b =>
    {
    await Task.CompletedTask;
    _logger.LogWarning($"Fallback: {b.Exception.Message}");
    }))
    // 熔断
    .AddPolicyHandler(Policy<HttpResponseMessage>.Handle<TimeoutRejectedException>().CircuitBreakerAsync(5, TimeSpan.FromSeconds(3), (ex, ts) =>
    {
    _logger.LogWarning($"Open Circuit Breaker:{ts.TotalMilliseconds}");
    }, () =>
    {
    _logger.LogWarning($"Closed Circuit Breaker");
    }, () =>
    {
    _logger.LogWarning($"HalfOpen Circuit Breaker");
    }))
    // 重试
    .AddPolicyHandler(Policy<HttpResponseMessage>
    .Handle<TimeoutRejectedException>()
    .WaitAndRetryAsync(
    new[]
    {
    TimeSpan.FromMilliseconds(100),
    TimeSpan.FromMilliseconds(200)
    }
    )
    )
    // 超时
    .AddPolicyHandler(Policy.TimeoutAsync<HttpResponseMessage>(TimeSpan.FromSeconds(0.5)));

    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    }

    说明(这部分代码在实际使用中建议重新封装,不应该每次都为当前定义的 HttpClient 设置一堆重复代码):

    • 通过 services.AddHttpClient 定义一个名为 githubHttpClient ,后续可通过名称获取到这个 HttpClient 对象来发送 Http 请求;
    • 通过 AddPolicyHandler其他扩展方法参考:Polly and HttpClientFactory AddTransientHttpErrorPolicyAddPolicyHandlerFromRegistry 的使用介绍) 为此 HttpClient 添加 Polly 策略;
    • 设置降级策略,当出现任何异常,返回 fallbackResponse
    • 设置熔断策略,当连续出现 TimeoutRejectedException 异常 5 次,熔断 3s;
    • 设置重试策略,当出现 TimeoutRejectedException 分别等待 100ms、200ms 后重试;
    • 设置超时策略,请求超时为 0.5s,超时默认会抛出 TimeoutRejectedException
    • 当多个策略叠加时,最先起作用的是最后添加的;
  4. 使用 HttpClient

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    public class ValuesController : ControllerBase
    {
    private readonly IHttpClientFactory _httpClientFactory;

    public ValuesController(IHttpClientFactory httpClientFactory)
    {
    _httpClientFactory = httpClientFactory;
    }

    [HttpGet]
    public async Task<ActionResult> Get()
    {
    var client = _httpClientFactory.CreateClient("github");
    var request = new HttpRequestMessage(HttpMethod.Get, "/");
    var response = await client.SendAsync(request);
    var result = await response.Content.ReadAsStringAsync();
    return Ok(result);
    }
    }

    说明:从 HttpClientFactory 中获取定义好的名为 githubHttpClient 对象,和普通的 HttpClient 的区别是此 HttpClient 已具有定义的各种 Polly 策略,其他没任何区别;

  5. 效果测试

    Timeout Retry

    Retry

    Timeout Circuit Breaker

    Open

    HalfOpen

    Closed

    Fallback

    Fallback

参考链接

如果对你有帮助就好