feat(backend): start work on metrics

Foxnouns.Backend/Config.cs

@@ -10,6 +10,7 @@ public class Config
     public string MediaBaseUrl { get; set; } = null!;
 
     public string Address => $"http://{Host}:{Port}";
+    public string? MetricsAddress => Logging.MetricsPort != null ? $"http://{Host}:{Logging.MetricsPort}" : null;
 
     public LoggingConfig Logging { get; init; } = new();
     public DatabaseConfig Database { get; init; } = new();
@@ -27,6 +28,7 @@ public class Config
         public bool SentryTracing { get; init; } = false;
         public double SentryTracesSampleRate { get; init; } = 0.0;
         public bool LogQueries { get; init; } = false;
+        public int? MetricsPort { get; init; }
     }
 
     public class DatabaseConfig

Foxnouns.Backend/Extensions/WebApplicationExtensions.cs

@@ -1,3 +1,6 @@
+using App.Metrics;
+using App.Metrics.AspNetCore;
+using App.Metrics.Formatters.Prometheus;
 using Foxnouns.Backend.Database;
 using Foxnouns.Backend.Jobs;
 using Foxnouns.Backend.Middleware;
@@ -6,6 +9,7 @@ using Microsoft.EntityFrameworkCore;
 using NodaTime;
 using Serilog;
 using Serilog.Events;
+using IClock = NodaTime.IClock;
 
 namespace Foxnouns.Backend.Extensions;
 
@@ -29,6 +33,7 @@ public static class WebApplicationExtensions
             .MinimumLevel.Override("Microsoft.AspNetCore.Hosting", LogEventLevel.Warning)
             .MinimumLevel.Override("Microsoft.AspNetCore.Mvc", LogEventLevel.Warning)
             .MinimumLevel.Override("Microsoft.AspNetCore.Routing", LogEventLevel.Warning)
+            .MinimumLevel.Override("Hangfire", LogEventLevel.Information)
             .WriteTo.Console();
 
         if (config.Logging.SeqLogUrl != null)
@@ -52,6 +57,36 @@ public static class WebApplicationExtensions
         return config;
     }
 
+    public static WebApplicationBuilder AddMetrics(this WebApplicationBuilder builder)
+    {
+        var config = builder.Configuration.Get<Config>() ?? new();
+        var metrics = AppMetrics.CreateDefaultBuilder()
+            .OutputMetrics.AsPrometheusPlainText()
+            .Build();
+
+        builder.Services.AddSingleton(metrics);
+        builder.Services.AddSingleton<IMetrics>(metrics);
+
+        builder.WebHost
+            .ConfigureMetrics(metrics)
+            .UseMetrics(opts =>
+            {
+                opts.EndpointOptions = options =>
+                {
+                    // Metrics must listen on a separate port for security reasons. If no metrics port is set, disable the endpoint entirely.
+                    options.MetricsEndpointEnabled = config.Logging.MetricsPort != null;
+                    options.EnvironmentInfoEndpointEnabled = config.Logging.MetricsPort != null;
+                    options.MetricsTextEndpointEnabled = false;
+                    options.MetricsEndpointOutputFormatter = metrics.OutputMetricsFormatters
+                        .OfType<MetricsPrometheusTextOutputFormatter>().First();
+                };
+            })
+            .UseMetricsWebTracking()
+            .ConfigureAppMetricsHostingConfiguration(opts => { opts.AllEndpointsPort = config.Logging.MetricsPort; });
+
+        return builder;
+    }
+
     public static IConfigurationBuilder AddConfiguration(this IConfigurationBuilder builder)
     {
         var file = Environment.GetEnvironmentVariable("FOXNOUNS_CONFIG_FILE") ?? "config.ini";

Foxnouns.Backend/Foxnouns.Backend.csproj

@@ -6,6 +6,9 @@
     </PropertyGroup>
 
     <ItemGroup>
+        <PackageReference Include="App.Metrics" Version="4.3.0" />
+        <PackageReference Include="App.Metrics.AspNetCore.All" Version="4.3.0" />
+        <PackageReference Include="App.Metrics.Prometheus" Version="4.3.0" />
         <PackageReference Include="EFCore.NamingConventions" Version="8.0.3"/>
         <PackageReference Include="Hangfire.AspNetCore" Version="1.8.14" />
         <PackageReference Include="Hangfire.Core" Version="1.8.14" />

Foxnouns.Backend/Metrics.cs

@@ -0,0 +1,6 @@
+namespace Foxnouns.Backend;
+
+public static class Metrics
+{
+    
+}

Foxnouns.Backend/Program.cs

@@ -21,7 +21,7 @@ var builder = WebApplication.CreateBuilder(args);
 
 var config = builder.AddConfiguration();
 
-builder.AddSerilog();
+builder.AddSerilog().AddMetrics();
 
 builder.WebHost
     .UseSentry(opts =>
@@ -103,6 +103,7 @@ app.UseHangfireDashboard("/hangfire", new DashboardOptions
 
 app.Urls.Clear();
 app.Urls.Add(config.Address);
+if (config.MetricsAddress != null) app.Urls.Add(config.MetricsAddress);
 
 // Fire off the periodic tasks loop in the background
 _ = new Timer(_ =>

Foxnouns.Backend/config.example.ini

@@ -20,6 +20,8 @@ SentryTracing = true
 SentryTracesSampleRate = 1.0
 ; Whether to log SQL queries. Note that this is very verbose. Defaults to false.
 LogQueries = false
+; The port the /metrics endpoint will listen on. If not set, metrics will be disabled.
+MetricsPort = 5001
 
 [Database]
 ; The database URL in ADO.NET format.