Add some metrics (more to come)

src/FakeRelay.Web/Controllers/ApiController.cs

@@ -2,12 +2,15 @@ using System.Collections.Immutable;
 using FakeRelay.Core.Helpers;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Caching.Memory;
+using Prometheus;
 
 namespace FakeRelay.Web.Controllers;
 
 public class ApiController : Controller
 {
     private readonly IMemoryCache _memoryCache;
+    private static readonly Counter IndexRequests =
+        Metrics.CreateCounter("index_requests", "Requests to index statuses", "instance");
 
     public ApiController(IMemoryCache memoryCache)
     {
@@ -46,6 +49,7 @@ public class ApiController : Controller
         }
         
         var response = await MastodonHelper.EnqueueStatusToFetchAsync(host, statusUrl);
+        IndexRequests.WithLabels(host).Inc();
         Response.Headers["instance"] = host;
         return Content(response, "application/activity+json");
     }

src/FakeRelay.Web/FakeRelay.Web.csproj

@@ -4,6 +4,10 @@
     <ProjectReference Include="..\FakeRelay.Core\FakeRelay.Core.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="prometheus-net.AspNetCore" Version="7.0.0" />
+  </ItemGroup>
+
   <PropertyGroup>
     <TargetFramework>net6.0</TargetFramework>
     <Nullable>enable</Nullable>

src/FakeRelay.Web/Program.cs

@@ -1,6 +1,7 @@
 using FakeRelay.Core;
 using FakeRelay.Web.Services;
 using Microsoft.AspNetCore.HttpOverrides;
+using Prometheus;
 
 var webApplicationOptions = new WebApplicationOptions
 {
@@ -48,4 +49,9 @@ app.MapControllerRoute(
     "default",
     "{controller=Home}/{action=Index}/{id?}");
 
+app.UseEndpoints(endpoints =>
+{
+    endpoints.MapMetrics();
+});
+
 app.Run();