Add Metrics (OpenTelemetry with Prometheus Export endpoint) (#2010)

* add metrics in opentelemetry standard, uses built-in aspnetcore metrics, built-in npgsql metrics, and exports in prometheus format

* make metrics enabled by default, but disableable in appsettings

* link to metrics on diagnostics page if enabled

* use uppercase convention /Metrics instead of /metrics

* use a service extension method to follow conventions

Directory.Packages.props

@@ -27,6 +27,8 @@
     <PackageVersion Include="Namotion.Reflection" Version="3.1.1" />
     <PackageVersion Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="8.0.4" />
     <PackageVersion Include="NSubstitute" Version="5.1.0" />
+    <PackageVersion Include="OpenTelemetry.Exporter.Prometheus.AspNetCore" Version="1.9.0-beta.2" />
+    <PackageVersion Include="OpenTelemetry.Extensions.Hosting" Version="1.9.0" />
     <PackageVersion Include="RoslynCodeTaskFactory" Version="2.0.7" />
     <PackageVersion Include="Serilog.AspNetCore" Version="8.0.1" />
     <PackageVersion Include="SharpCompress" Version="0.36.0" />

TASVideos.Core/Settings/AppSettings.cs

@@ -28,6 +28,8 @@ public class AppSettings
 
 	public ReCaptchaSettings ReCaptcha { get; set; } = new();
 
+	public bool EnableMetrics { get; set; }
+
 	// User is only allowed to submit X submissions in Y days
 	public class SubmissionRateLimit
 	{

TASVideos/Extensions/ApplicationBuilderExtensions.cs

@@ -112,6 +112,14 @@ public static IApplicationBuilder UseMvcWithOptions(this IApplicationBuilder app
 		return app.UseEndpoints(endpoints =>
 		{
 			endpoints.MapRazorPages();
+
+			if (settings.EnableMetrics)
+			{
+				endpoints.MapPrometheusScrapingEndpoint().RequireAuthorization(builder =>
+				{
+					builder.RequireClaim(CustomClaimTypes.Permission, ((int)PermissionTo.SeeDiagnostics).ToString());
+				});
+			}
 		});
 	}
 }

TASVideos/Extensions/ServiceCollectionExtensions.cs

@@ -4,6 +4,7 @@
 using Microsoft.AspNetCore.Localization;
 using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.AspNetCore.ResponseCompression;
+using OpenTelemetry.Metrics;
 using TASVideos.Core.Settings;
 using TASVideos.TagHelpers;
 
@@ -161,4 +162,30 @@ private static IServiceCollection AddHttpContext(this IServiceCollection service
 			.AddSingleton<IHttpContextAccessor, HttpContextAccessor>()
 			.AddTransient(provider => provider.GetRequiredService<IHttpContextAccessor>().HttpContext!.User);
 	}
+
+	public static IServiceCollection AddMetrics(this IServiceCollection services, AppSettings settings)
+	{
+		if (settings.EnableMetrics)
+		{
+			services
+				.AddOpenTelemetry()
+				.WithMetrics(builder =>
+				{
+					builder.AddMeter(
+						"Microsoft.AspNetCore.Hosting",
+						"Microsoft.AspNetCore.Server.Kestrel",
+						"Microsoft.AspNetCore.Routing",
+						"Microsoft.AspNetCore.Diagnostics");
+
+					builder.AddMeter("Npgsql");
+
+					builder.AddPrometheusExporter(options =>
+					{
+						options.ScrapeEndpointPath = "/Metrics";
+					});
+				});
+		}
+
+		return services;
+	}
 }

TASVideos/Pages/Diagnostics/Index.cshtml

@@ -40,6 +40,8 @@
 	<li><a asp-page="Logging">Logging</a></li>
 	<li><a asp-page="SendEmail">Send an Email</a></li>
 	<li><a asp-page="SystemPages">System Wiki Pages</a></li>
+	<li condition="@Settings.EnableMetrics"><a href="/Metrics">Metrics</a></li>
+	<li condition="[email protected]">Metrics (disabled)</li>
 </ul>
 
 <standard-table>

TASVideos/Program.cs

@@ -49,7 +49,8 @@
 		pipeline.AddScssBundle("/css/site.css", "/css/site.scss");
 		pipeline.AddScssBundle("/css/forum.css", "/css/forum.scss");
 		pipeline.AddFiles("text/javascript", "/js/*");
-	});
+	})
+	.AddMetrics(settings);
 
 builder.Host.UseSerilog();
 

TASVideos/TASVideos.csproj

@@ -42,6 +42,8 @@
 		<PackageReference Include="Microsoft.IO.RecyclableMemoryStream" />
 		<PackageReference Include="Microsoft.Web.LibraryManager.Build" />
 		<PackageReference Include="Namotion.Reflection" />
+		<PackageReference Include="OpenTelemetry.Exporter.Prometheus.AspNetCore" />
+		<PackageReference Include="OpenTelemetry.Extensions.Hosting" />
 		<PackageReference Include="RoslynCodeTaskFactory" />
 		<PackageReference Include="Serilog.AspNetCore" />
 	</ItemGroup>

TASVideos/appsettings.json

@@ -13,5 +13,6 @@
   "webOptimizer": {
     "enableCaching": true,
     "enableTagHelperBundling": true
-  }
+  },
+  "EnableMetrics": true
 }