Prometheus Metrics in C# (.NET): Integration and Configuration

Prometheus Metrics in C# (.NET): Complete Integration Guide

Prometheus is an open-source monitoring system that collects and stores metrics as time series data. For C# (.NET) developers, integrating with Prometheus opens the ability to track application performance, business metrics, and system health in real time. In this article, we will cover how to connect Prometheus to a .NET application, which libraries to use, and how to properly configure metrics.

Why Do You Need Prometheus Metrics in .NET?

Monitoring with Prometheus allows you to:

• Track the number of requests, errors, and response time.
• Collect performance metrics (CPU, memory, GC).
• Create custom business metrics (active users, orders).
• Integrate with Grafana for dashboard visualization.
• Set up alerts based on threshold values.

The prometheus-net Library

The main library for working with Prometheus in .NET is prometheus-net. It supports ASP.NET Core, .NET Core, .NET Framework, and gRPC. Install via NuGet:

dotnet add package prometheus-net

For ASP.NET Core, additionally install:

dotnet add package prometheus-net.AspNetCore

Metric Types in Prometheus

The library supports all standard metric types:

• Counter — a counter that only increases (number of requests).
• Gauge — a value that can increase and decrease (current temperature).
• Histogram — a histogram for measuring value distribution (response time).
• Summary — quantiles for data aggregation (p95, p99).

Example: Basic Counter

Let's create a metric that counts the number of requests to an endpoint:

using Prometheus;

public class MetricsService{    private static readonly Counter RequestCount = Metrics        .CreateCounter("app_requests_total", "Total number of requests", new CounterConfiguration        {            LabelNames = new[] { "method", "endpoint" }        });

    public void RecordRequest(string method, string endpoint)    {        RequestCount.WithLabels(method, endpoint).Inc();    }}

In an ASP.NET Core controller, the call would look like this:

[ApiController][Route("api/order")]public class OrderController : ControllerBase{    private readonly MetricsService _metrics;

    public OrderController(MetricsService metrics) => _metrics = metrics;

    [HttpGet]    public IActionResult GetOrders()    {        _metrics.RecordRequest("GET", "/api/order");        return Ok(new { orders = new[] { "order1", "order2" } });    }}

Example: Gauge for Active Users

private static readonly Gauge ActiveUsers = Metrics    .CreateGauge("app_active_users", "Number of active users");

public void UserLoggedIn() => ActiveUsers.Inc();public void UserLoggedOut() => ActiveUsers.Dec();

Example: Histogram for Response Time

private static readonly Histogram RequestDuration = Metrics    .CreateHistogram("app_request_duration_seconds", "Request duration in seconds",        new HistogramConfiguration        {            Buckets = Histogram.ExponentialBuckets(0.001, 2, 10) // from 1ms to ~1s        });

public void RecordRequestDuration(double seconds){    RequestDuration.Observe(seconds);}

Exporting Metrics in ASP.NET Core

To allow Prometheus to collect metrics, you need to add the /metrics endpoint. In Program.cs:

using Prometheus;

var builder = WebApplication.CreateBuilder(args);builder.Services.AddCont