Telemetry improvements

src/web/CareLeavers.Web/Program.cs

@@ -3,11 +3,13 @@
 using CareLeavers.Web.Caching;
 using CareLeavers.Web.Configuration;
 using CareLeavers.Web.ContentfulRenderers;
+using CareLeavers.Web.Telemetry;
 using Contentful.AspNetCore;
 using Contentful.Core;
 using Contentful.Core.Models;
 using GovUk.Frontend.AspNetCore;
 using Microsoft.Extensions.Caching.Distributed;
+using OpenTelemetry.Trace;
 using Serilog;
 
 Log.Logger = new LoggerConfiguration()
@@ -24,14 +26,21 @@
     builder.Services.AddSerilog((_, lc) => lc
         .ConfigureLogging(builder.Configuration["ApplicationInsights:ConnectionString"]));
 
-    var connString = builder.Configuration.GetValue<string>("ApplicationInsights:ConnectionString");
+    var appInsightsConnectionString = builder.Configuration.GetValue<string>("ApplicationInsights:ConnectionString");
 
-    if (!string.IsNullOrEmpty(connString))
+    if (!string.IsNullOrEmpty(appInsightsConnectionString))
     {
         builder.Services.AddOpenTelemetry()
-            .UseAzureMonitor(x => x.ConnectionString = connString);
+            .WithTracing(x =>
+            {
+                x.AddAspNetCoreInstrumentation();
+                x.AddProcessor<RouteTelemetryProcessor>();
+            })
+            .UseAzureMonitor(x => x.ConnectionString = appInsightsConnectionString);
     }
 
+    builder.Services.AddHttpContextAccessor();
+
     builder.Services.AddContentful(builder.Configuration);
 
     builder.Services.AddTransient<HtmlRenderer>((c) =>

src/web/CareLeavers.Web/Telemetry/RouteTelemetryProcessor.cs

@@ -0,0 +1,28 @@
+using System.Diagnostics;
+using OpenTelemetry;
+
+namespace CareLeavers.Web.Telemetry;
+
+public class RouteTelemetryProcessor(IHttpContextAccessor httpContextAccessor) : BaseProcessor<Activity>
+{
+    public override void OnEnd(Activity activity)
+    {
+        var httpContext = httpContextAccessor.HttpContext;
+
+        if (httpContext == null)
+        {
+            base.OnEnd(activity);
+            return;
+        }
+
+        var routeData = httpContext.GetRouteData();
+        routeData.Values.TryGetValue("slug", out var slug);
+
+        if (slug != null)
+        {
+            activity.SetTag("http.route", $"/{slug}");
+        }
+
+        base.OnEnd(activity);
+    }
+}