在Polly v8的OnOpened回调中识别触发熔断的HttpClient

1. 修改策略工厂，接收客户端名称参数 #

让策略工厂的创建方法支持传入HttpClient的名称，确保每个客户端的熔断策略能关联到自身标识：

public ResiliencePipeline<HttpResponseMessage> Create(string clientName)
{
    var builder = new ResiliencePipelineBuilder<HttpResponseMessage>()
        .AddTimeout(MapToTimeoutStrategyOptions())
        // 将客户端名称传入熔断策略配置
        .AddCircuitBreaker(MapToHttpCircuitBreakerStrategyOptions(clientName))
        .AddRetry(MapToServiceNowHttpRetryStrategyOptions());
    
    // 补上缺失的Build()调用，返回构建好的策略管道
    return builder.Build();
}

2. 在DI配置中传递HttpClient名称 #

利用AddResilienceHandler提供的上下文（AddResilienceHandlerContext），直接获取当前HttpClient的名称并传给策略工厂：

services
    .AddHttpClient("ClientA")
    .AddResilienceHandler("ClientA", (builder, context) =>
    {
        var strategyFactory = context.ServiceProvider.GetRequiredService<IResiliencyStrategyFactory>();
        // context.ServiceName就是当前HttpClient的命名（"ClientA"）
        builder.AddPipeline(strategyFactory.Create(context.ServiceName));
    });

services
    .AddHttpClient("ClientB")
    .AddResilienceHandler("ClientB", (builder, context) =>
    {
        var strategyFactory = context.ServiceProvider.GetRequiredService<IResiliencyStrategyFactory>();
        builder.AddPipeline(strategyFactory.Create(context.ServiceName));
    });

3. 调整熔断策略配置，关联客户端名称 #

修改熔断策略的配置方法，接收客户端名称参数，在回调中直接使用该标识反馈故障：

private HttpCircuitBreakerStrategyOptions MapToHttpCircuitBreakerStrategyOptions(string clientName) =>
    new()
    {
        MinimumThroughput = resiliencyConfig.CircuitBreakerConfig.Throughput,
        FailureRatio = resiliencyConfig.CircuitBreakerConfig.FailureRatio,
        SamplingDuration = TimeSpan.FromSeconds(resiliencyConfig.CircuitBreakerConfig.SamplingDuration),
        BreakDuration = TimeSpan.FromSeconds(resiliencyConfig.CircuitBreakerConfig.DurationOfBreakSeconds),
        OnClosed = args =>
        {
            // 反馈指定客户端已恢复
            Console.WriteLine($"客户端 {clientName} 熔断状态已关闭，服务恢复正常");
            return Task.CompletedTask;
        },
        OnOpened = args =>
        {
            // 反馈指定客户端触发熔断
            Console.WriteLine($"客户端 {clientName} 已触发熔断，服务暂时不可用");
            return Task.CompletedTask;
        }
    };

（可选）通过OperationKey传递标识 #

如果你想通过OnCircuitOpenedArguments的OperationKey属性获取客户端名称，可以在DI配置的策略构建阶段，给ResilienceContext设置默认的OperationKey：

services
    .AddHttpClient("ClientA")
    .AddResilienceHandler("ClientA", (builder, context) =>
    {
        var strategyFactory = context.ServiceProvider.GetRequiredService<IResiliencyStrategyFactory>();
        builder.AddPipeline(strategyFactory.Create())
               // 设置默认OperationKey为当前HttpClient名称
               .Configure(resilienceContext => resilienceContext.OperationKey = context.ServiceName);
    });

此时在熔断回调中就可以通过args.Context.OperationKey获取客户端名称：

OnOpened = args =>
{
    string clientName = args.Context.OperationKey;
    Console.WriteLine($"客户端 {clientName} 已触发熔断");
    return Task.CompletedTask;
}

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