如何在.NET Core Azure函数中用Polly实现动态抖动退避等待重试

我正在实现带抖动的等待重试，但当前示例中的延迟是固定的，想让延迟实现动态化。

当前固定延迟的示例代码：

var delay = Backoff.DecorrelatedJitterBackoffV2(medianFirstRetryDelay: TimeSpan.FromSeconds(1), retryCount: 3);
var retryPolicy = Policy.Handle<FooException>().WaitAndRetryAsync(delay);

我的项目基于Azure函数，现有DI相关代码如下：

public class Startup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        var configuration = builder.GetContext().Configuration;
        builder.Services.RegisterService(configuration);
    }
}

public static IHttpClientBuilder RegisterService(this IServiceCollection serviceCollection,IConfiguration configuration)
{
    return serviceCollection.AddHttpClient<IService, Service>()
               .AddPolicyHandler(RetryPolicyHandler.GetRetryPolicy())
}

public static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy(IConfiguration configuration)
{
    var delay =Backoff.DecorrelatedJitterBackoffV2(medianFirstRetryDelay: TimeSpan.FromSeconds(1), retryCount: 3);
    return HttpPolicyExtensions.HandleTransientHttpError().WaitAndRetryAsync(delay);
}

解决方案：通过配置驱动实现动态延迟 #

1. 从配置读取重试参数

在Azure函数的配置源（如local.settings.json或Azure门户配置）中添加重试相关参数，示例：

{
  "Values": {
    "Retry:MedianFirstRetryDelaySeconds": "2", // 首次重试的中位数延迟（秒）
    "Retry:RetryCount": "5" // 最大重试次数
  }
}

2. 修改重试策略代码，动态生成延迟序列

修正RegisterService方法的参数传递问题，并在GetRetryPolicy中从配置读取参数：

public static IHttpClientBuilder RegisterService(this IServiceCollection serviceCollection, IConfiguration configuration)
{
    // 确保将configuration传入GetRetryPolicy
    return serviceCollection.AddHttpClient<IService, Service>()
               .AddPolicyHandler(RetryPolicyHandler.GetRetryPolicy(configuration));
}

public static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy(IConfiguration configuration)
{
    // 从配置读取参数，设置默认值避免配置缺失报错
    var medianFirstRetryDelay = TimeSpan.FromSeconds(
        configuration.GetValue<double>("Retry:MedianFirstRetryDelaySeconds", 1));
    var retryCount = configuration.GetValue<int>("Retry:RetryCount", 3);

    // 动态生成带抖动的延迟序列
    var delay = Backoff.DecorrelatedJitterBackoffV2(
        medianFirstRetryDelay: medianFirstRetryDelay, 
        retryCount: retryCount);
        
    return HttpPolicyExtensions.HandleTransientHttpError().WaitAndRetryAsync(delay);
}

3. 可选：支持运行时动态更新配置（进阶）

如果需要在不重启函数的情况下更新重试参数，可以结合IOptionsMonitor<T>来读取配置。此时需要将重试策略封装为可动态获取的类型：

public class RetrySettings
{
    public double MedianFirstRetryDelaySeconds { get; set; } = 1;
    public int RetryCount { get; set; } = 3;
}

// 在Startup中绑定配置
builder.Services.Configure<RetrySettings>(configuration.GetSection("Retry"));

// 修改策略获取方式
public static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy(IOptionsMonitor<RetrySettings> settingsMonitor)
{
    var settings = settingsMonitor.CurrentValue;
    var delay = Backoff.DecorrelatedJitterBackoffV2(
        medianFirstRetryDelay: TimeSpan.FromSeconds(settings.MedianFirstRetryDelaySeconds), 
        retryCount: settings.RetryCount);
        
    return HttpPolicyExtensions.HandleTransientHttpError().WaitAndRetryAsync(delay);
}

// 注册时注入IOptionsMonitor
public static IHttpClientBuilder RegisterService(this IServiceCollection serviceCollection)
{
    return serviceCollection.AddHttpClient<IService, Service>()
               .AddPolicyHandler((sp, req) => 
                   RetryPolicyHandler.GetRetryPolicy(sp.GetRequiredService<IOptionsMonitor<RetrySettings>>()));
}

这种方式下，当配置更新时，IOptionsMonitor会自动获取最新值，下次创建策略时使用新参数。

内容的提问来源于stack exchange，提问作者itaustralia