OpenTelemetry下ASP.NET Core自定义Prometheus指标未被采集求助

我在ASP.NET Core应用中实现了自定义中间件，用于通过Prometheus记录HTTP请求指标prometheus_demo_request_total。每个HTTP请求都会触发该中间件，且已确认counter.Labels(...).Inc()调用在中间件执行时正常运行，但访问/metrics端点时仅能看到OpenTelemetry的默认指标，自定义指标完全未出现。需要排查问题根源，确保自定义指标能被Prometheus正确采集展示。

Startup.cs 代码 #

public void ConfigureServices(IServiceCollection services)
{
    ...

    services.AddOpenTelemetry()
                .WithMetrics(builder => builder
                    .AddRuntimeInstrumentation()
                    .AddAspNetCoreInstrumentation()
                    .AddHttpClientInstrumentation()
                    .AddPrometheusExporter());
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, CustomDbContext dbContext, ILogger<RedactableDbContext> logger)
{
    app.UseRequestMiddleware();

    ...
}

使用的相关NuGet包 #

<PackageReference Include="OpenTelemetry.Exporter.Console" Version="1.6.0" />
<PackageReference Include="OpenTelemetry.Exporter.OpenTelemetryProtocol" Version="1.6.0" />
<PackageReference Include="OpenTelemetry.Exporter.Prometheus.AspNetCore" Version="1.6.0-rc.1" />
<PackageReference Include="OpenTelemetry.Extensions.Hosting" Version="1.6.0" />
<PackageReference Include="OpenTelemetry.Instrumentation.AspNetCore" Version="1.5.1-beta.1" />
<PackageReference Include="OpenTelemetry.Instrumentation.Http" Version="1.5.1-beta.1" />
<PackageReference Include="OpenTelemetry.Instrumentation.RunTime" Version="1.5.1" />
<PackageReference Include="prometheus-net.AspNetCore" Version="8.2.0" />

核心问题排查点 #

• 库体系冲突：同时引用OpenTelemetry.Exporter.Prometheus.AspNetCore和prometheus-net.AspNetCore，两者各自维护独立的指标体系和/metrics端点，OpenTelemetry的exporter无法读取prometheus-net创建的指标，导致自定义指标无法被采集。
• 指标API不兼容：参考的实现大概率是基于prometheus-net原生API创建的Counter，但OpenTelemetry的Prometheus exporter仅识别通过OpenTelemetry API创建的指标，两套API互不兼容。

解决方案 #

方案一：统一使用OpenTelemetry API创建自定义指标 #

1. 修改ConfigureServices配置：注册自定义Meter

services.AddOpenTelemetry()
    .WithMetrics(builder => builder
        .AddRuntimeInstrumentation()
        .AddAspNetCoreInstrumentation()
        .AddHttpClientInstrumentation()
        .AddPrometheusExporter()
        .AddMeter("PrometheusDemo")); // 添加自定义Meter名称

2. 重构中间件使用OpenTelemetry指标API

public class RequestMiddleware
{
    private readonly RequestDelegate _next;
    private readonly Counter<long> _requestCounter;

    public RequestMiddleware(RequestDelegate next, IMeterFactory meterFactory)
    {
        _next = next;
        var meter = meterFactory.Create("PrometheusDemo");
        _requestCounter = meter.CreateCounter<long>(
            "prometheus_demo_request_total", 
            description: "Total number of HTTP requests");
    }

    public async Task InvokeAsync(HttpContext context)
    {
        // 可按需添加标签维度，如请求方法、路径
        _requestCounter.Add(1, 
            new KeyValuePair<string, object>("method", context.Request.Method),
            new KeyValuePair<string, object>("endpoint", context.Request.Path));
        await _next(context);
    }
}

3. 移除冲突包：删除prometheus-net.AspNetCore的NuGet引用，避免端点冲突。

方案二：统一使用prometheus-net，移除OpenTelemetry Prometheus Exporter #

1. 修改ConfigureServices配置：注册prometheus-net服务

// 注册prometheus-net指标端点
services.AddMetricServer();
// 注册自定义Counter
services.AddSingleton<Counter>(sp => 
    Metrics.CreateCounter("prometheus_demo_request_total", "Total number of HTTP requests"));

2. 中间件保持prometheus-net原生用法

public class RequestMiddleware
{
    private readonly RequestDelegate _next;
    private readonly Counter _requestCounter;

    public RequestMiddleware(RequestDelegate next, Counter requestCounter)
    {
        _next = next;
        _requestCounter = requestCounter;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        _requestCounter.Labels(context.Request.Method, context.Request.Path).Inc();
        await _next(context);
    }
}

3. 移除冲突配置和包：删除AddPrometheusExporter()配置，以及OpenTelemetry.Exporter.Prometheus.AspNetCore的NuGet引用。

内容的提问来源于stack exchange，提问作者Ammar