在.net8中使用OpenTelemetry来metric

　　OpenTelemetry可以说是可观测性里的中流砥柱，自然.net也能很好的与期交互。OpenTelemetry支持了很多语言，C#也在其中，下面的列子就是在一个api项目中，添加对OpenTelemetry的NuGet包的引用，来完成应用的metric的。

　　基本思路是，第一步：在程序中引入OpenTelemetry相关包，并配置；第二步，下载Prometheus，配置采集该程序的性能指标；第三中，下载Grafana，可视化展示采集到的指示。

　　具体使用Prometheus和Grafana我以前的公众号文章中有说到，也可以参照微软官方ASP.NET Core 指标 | Microsoft Learn来了解上体使用步骤。其中的Custom是自定义的指标，可以与业务的api中埋点来计数。

using APIMetricDemo;
using OpenTelemetry.Metrics;
using OpenTelemetry.Resources;
using System.Diagnostics.Metrics;
using OpenTelemetry.Exporter;
using OpenTelemetry.Instrumentation.AspNetCore;
using OpenTelemetry.Instrumentation.Http;
using OpenTelemetry.AutoInstrumentation.Instrumentations;
using OpenTelemetry.Logs;
using OpenTelemetry.Trace;

var builder = WebApplication.CreateSlimBuilder(args);
builder.Services.AddOpenTelemetry().WithMetrics(builder =>
{
    builder.AddAspNetCoreInstrumentation();
    builder.AddPrometheusExporter();
    builder.AddHttpClientInstrumentation();
    builder.AddProcessInstrumentation();
    builder.AddRuntimeInstrumentation();
    builder.AddPrometheusHttpListener();
    builder.AddMeter("Microsoft.AspNetCore.Hosting", "Microsoft.AspNetCore.Server.Kestrel", "Custome");
    builder.AddView("http-server-request-duration", new ExplicitBucketHistogramConfiguration
    {
        Boundaries = new double[] { 0, 0.005, 0.01, 0.025, 0.05,
                       0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10 }
    });
});
var app = builder.Build();
app.MapPrometheusScrapingEndpoint();
var sampleTodos = TodoGenerator.GenerateTodos().ToArray();
var todosApi = app.MapGroup("/todos");
todosApi.MapGet("/", () =>
{
    DiagnosticsConfig.RequestCounter.Add(1,
        new("Path", "/todos"),
        new("Method", "get"));
    return sampleTodos;
});
todosApi.MapGet("/{id}", (int id) =>
    sampleTodos.FirstOrDefault(a => a.Id == id) is { } todo
        ? Results.Ok(todo)
        : Results.NotFound());
app.Run();
public static class DiagnosticsConfig
{
    public const string ServiceName = "Custome";
    public static Meter Meter = new(ServiceName);
    public static Counter<long> RequestCounter =
        Meter.CreateCounter<long>("getTodos_count");
}