feat(observability): add Seq logging sink and OpenTelemetry tracing

- Add Serilog.Sinks.Seq to ship structured logs to Seq
- Add OpenTelemetry with ASP.NET Core + HttpClient instrumentation
- Export traces to Seq via OTLP (http://localhost:5341/ingest/otlp)
- Enrich Serilog logs with TraceId/SpanId from Activity.Current
- Register AddCceOpenTelemetry in both External and Internal APIs
- Add Seq configuration section to appsettings.json (empty in prod, localhost in dev)
- Keep existing Prometheus metrics untouched

Author: rashed99mm

backend/src/CCE.Api.Common/CCE.Api.Common.csproj

@@ -38,6 +38,12 @@
     <PackageReference Include="Sentry.Serilog" />
     <PackageReference Include="prometheus-net" />
     <PackageReference Include="prometheus-net.AspNetCore" />
+    <PackageReference Include="Serilog.Sinks.Seq" />
+    <PackageReference Include="OpenTelemetry" />
+    <PackageReference Include="OpenTelemetry.Exporter.OpenTelemetryProtocol" />
+    <PackageReference Include="OpenTelemetry.Extensions.Hosting" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.AspNetCore" />
+    <PackageReference Include="OpenTelemetry.Instrumentation.Http" />
   </ItemGroup>
 
   <ItemGroup>

backend/src/CCE.Api.Common/Observability/LoggingExtensions.cs

@@ -2,8 +2,11 @@
 using Microsoft.Extensions.Hosting;
 using Sentry.Serilog;
 using Serilog;
+using Serilog.Core;
 using Serilog.Events;
 using Serilog.Formatting.Compact;
+using Serilog.Sinks.Seq;
+using System.Diagnostics;
 
 namespace CCE.Api.Common.Observability;
 
@@ -32,6 +35,7 @@ public static IHostBuilder UseCceSerilog(this IHostBuilder builder)
                 .MinimumLevel.Override("Microsoft.AspNetCore", LogEventLevel.Warning)
                 .MinimumLevel.Override("Microsoft.EntityFrameworkCore", LogEventLevel.Warning)
                 .Enrich.FromLogContext()
+                .Enrich.With(new TraceIdEnricher())
                 .Enrich.WithProperty("app", ctx.HostingEnvironment.ApplicationName)
                 .Enrich.WithProperty("env", ctx.HostingEnvironment.EnvironmentName)
                 .WriteTo.Console(new CompactJsonFormatter());
@@ -49,6 +53,13 @@ public static IHostBuilder UseCceSerilog(this IHostBuilder builder)
             {
                 cfg.WriteTo.Sentry(o => ConfigureSentry(o, sentryDsn, ctx.Configuration, ctx.HostingEnvironment.EnvironmentName));
             }
+
+            var seqUrl = ctx.Configuration["Seq:ServerUrl"];
+            var seqApiKey = ctx.Configuration["Seq:ApiKey"];
+            if (!string.IsNullOrWhiteSpace(seqUrl))
+            {
+                cfg.WriteTo.Seq(seqUrl, apiKey: seqApiKey);
+            }
         });
     }
 
@@ -77,6 +88,21 @@ public static void ConfigureSentry(
         options.MinimumBreadcrumbLevel = LogEventLevel.Information;
     }
 
+    private sealed class TraceIdEnricher : ILogEventEnricher
+    {
+        public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
+        {
+            var activity = Activity.Current;
+            if (activity is null)
+            {
+                return;
+            }
+
+            logEvent.AddPropertyIfAbsent(propertyFactory.CreateProperty("TraceId", activity.TraceId.ToString()));
+            logEvent.AddPropertyIfAbsent(propertyFactory.CreateProperty("SpanId", activity.SpanId.ToString()));
+        }
+    }
+
     private static LogEventLevel? ParseLevel(string? value)
         => Enum.TryParse<LogEventLevel>(value, ignoreCase: true, out var lvl) ? lvl : null;
 }

backend/src/CCE.Api.Common/Observability/OpenTelemetryExtensions.cs

@@ -0,0 +1,45 @@
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using OpenTelemetry.Resources;
+using OpenTelemetry.Trace;
+using System;
+
+namespace CCE.Api.Common.Observability;
+
+/// <summary>
+/// Registers OpenTelemetry tracing for ASP.NET Core and HttpClient,
+/// exporting spans to Seq via OTLP. Disabled when Seq:EnableTracing is false
+/// or Seq:OtlpEndpoint is missing.
+/// </summary>
+public static class OpenTelemetryExtensions
+{
+    public static IServiceCollection AddCceOpenTelemetry(
+        this IServiceCollection services,
+        IConfiguration configuration,
+        string serviceName)
+    {
+        var otlpEndpoint = configuration["Seq:OtlpEndpoint"] ?? "http://localhost:5341/ingest/otlp";
+        var enableTracing = configuration.GetValue<bool?>("Seq:EnableTracing") ?? true;
+
+        if (!enableTracing || string.IsNullOrWhiteSpace(otlpEndpoint))
+        {
+            return services;
+        }
+
+        services.AddOpenTelemetry()
+            .WithTracing(tracing =>
+            {
+                tracing
+                    .SetResourceBuilder(ResourceBuilder.CreateDefault().AddService(serviceName))
+                    .AddAspNetCoreInstrumentation()
+                    .AddHttpClientInstrumentation()
+                    .AddSource("CCE")
+                    .AddOtlpExporter(opts =>
+                    {
+                        opts.Endpoint = new Uri(otlpEndpoint);
+                    });
+            });
+
+        return services;
+    }
+}

backend/src/CCE.Api.External/Program.cs

@@ -44,6 +44,7 @@
     .AddCcePermissionPolicies()
     .AddCceUserSync()
     .AddCceHealthChecks(builder.Configuration)
+    .AddCceOpenTelemetry(builder.Configuration, "CCE.Api.External")
     .AddCceOpenApi("CCE External API");
 
 builder.Services.AddHttpContextAccessor();

backend/src/CCE.Api.External/appsettings.Development.json

@@ -85,5 +85,8 @@
   },
   "Media": {
     "BaseUrl": "https://cce-external-api.runasp.net/media/"
+  },
+  "Seq": {
+    "ServerUrl": "http://localhost:5341"
   }
 }

backend/src/CCE.Api.External/appsettings.json

@@ -67,5 +67,11 @@
       "application/vnd.ms-excel",
       "application/msword"
     ]
+  },
+  "Seq": {
+    "ServerUrl": "",
+    "ApiKey": "",
+    "OtlpEndpoint": "http://localhost:5341/ingest/otlp",
+    "EnableTracing": true
   }
 }

backend/src/CCE.Api.Internal/Program.cs

@@ -36,6 +36,7 @@
     .AddCcePermissionPolicies()
     .AddCceUserSync()
     .AddCceHealthChecks(builder.Configuration)
+    .AddCceOpenTelemetry(builder.Configuration, "CCE.Api.Internal")
     .AddCceRateLimiter(builder.Configuration)
     .AddCceOpenApi("CCE Internal API");
 

backend/src/CCE.Api.Internal/appsettings.Development.json

@@ -72,5 +72,8 @@
   },
   "Media": {
     "BaseUrl": "https://cce-internal-api.runasp.net/media/"
+  },
+  "Seq": {
+    "ServerUrl": "http://localhost:5341"
   }
 }

backend/src/CCE.Api.Internal/appsettings.json

@@ -67,5 +67,11 @@
       "application/vnd.ms-excel",
       "application/msword"
     ]
+  },
+  "Seq": {
+    "ServerUrl": "",
+    "ApiKey": "",
+    "OtlpEndpoint": "http://localhost:5341/ingest/otlp",
+    "EnableTracing": true
   }
 }