[examples] Add manual activities and custom metrics to ASP.NET Core example (#4133)

examples/AspNetCore/Controllers/WeatherForecastController.cs

@@ -16,6 +16,9 @@
 
 namespace Examples.AspNetCore.Controllers;
 
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+using Examples.AspNetCore;
 using Microsoft.AspNetCore.Mvc;
 
 [ApiController]
@@ -24,16 +27,22 @@ public class WeatherForecastController : ControllerBase
 {
     private static readonly string[] Summaries = new[]
     {
-            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching",
+        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching",
     };
 
     private static readonly HttpClient HttpClient = new();
 
     private readonly ILogger<WeatherForecastController> logger;
+    private readonly ActivitySource activitySource;
+    private readonly Counter<long> freezingDaysCounter;
 
-    public WeatherForecastController(ILogger<WeatherForecastController> logger)
+    public WeatherForecastController(ILogger<WeatherForecastController> logger, Instrumentation instrumentation)
     {
         this.logger = logger ?? throw new ArgumentNullException(nameof(logger));
+
+        ArgumentNullException.ThrowIfNull(instrumentation);
+        this.activitySource = instrumentation.ActivitySource;
+        this.freezingDaysCounter = instrumentation.FreezingDaysCounter;
     }
 
     [HttpGet]
@@ -45,6 +54,17 @@ public class WeatherForecastController : ControllerBase
         // how dependency calls will be captured and treated
         // automatically as child of incoming request.
         var res = HttpClient.GetStringAsync("http://google.com").Result;
+
+        // Optional: Manually create an activity. This will become a child of
+        // the activity created from the instrumentation library for AspNetCore.
+        // Manually created activities are useful when there is a desire to track
+        // a specific subset of the request. In this example one could imagine
+        // that calculating the forecast is an expensive operation and therefore
+        // something to be distinguished from the overall request.
+        // Note: Tags can be added to the current activity without the need for
+        // a manual activity using Acitivty.Current?.SetTag()
+        using var activity = this.activitySource.StartActivity("calculate forecast");
+
         var rng = new Random();
         var forecast = Enumerable.Range(1, 5).Select(index => new WeatherForecast
         {
@@ -54,6 +74,9 @@ public class WeatherForecastController : ControllerBase
         })
         .ToArray();
 
+        // Optional: Count the freezing days
+        this.freezingDaysCounter.Add(forecast.Count(f => f.TemperatureC < 0));
+
         this.logger.LogInformation(
             "WeatherForecasts generated {count}: {forecasts}",
             forecast.Length,

examples/AspNetCore/Instrumentation.cs

@@ -0,0 +1,50 @@
+// <copyright file="Instrumentation.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+namespace Examples.AspNetCore;
+
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+
+/// <summary>
+/// It is recommended to use a custom type to hold references for
+/// ActivitySource and Instruments. This avoids possible type collisions
+/// with other components in the DI container.
+/// </summary>
+public class Instrumentation : IDisposable
+{
+    internal const string ActivitySourceName = "Examples.AspNetCore";
+    internal const string MeterName = "Examples.AspNetCore";
+    private readonly Meter meter;
+
+    public Instrumentation()
+    {
+        string? version = typeof(Instrumentation).Assembly.GetName().Version?.ToString();
+        this.ActivitySource = new ActivitySource(ActivitySourceName, version);
+        this.meter = new Meter(MeterName, version);
+        this.FreezingDaysCounter = this.meter.CreateCounter<long>("weather.days.freezing", "The number of days where the temperature is below freezing");
+    }
+
+    public ActivitySource ActivitySource { get; }
+
+    public Counter<long> FreezingDaysCounter { get; }
+
+    public void Dispose()
+    {
+        this.ActivitySource.Dispose();
+        this.meter.Dispose();
+    }
+}

examples/AspNetCore/Program.cs

@@ -14,7 +14,7 @@
 // limitations under the License.
 // </copyright>
 
-using System.Reflection;
+using Examples.AspNetCore;
 using OpenTelemetry;
 using OpenTelemetry.Exporter;
 using OpenTelemetry.Instrumentation.AspNetCore;
@@ -37,9 +37,13 @@ var logExporter = appBuilder.Configuration.GetValue<string>("UseLogExporter").To
 // Build a resource configuration action to set service information.
 Action<ResourceBuilder> configureResource = r => r.AddService(
     serviceName: appBuilder.Configuration.GetValue<string>("ServiceName"),
-    serviceVersion: Assembly.GetExecutingAssembly().GetName().Version?.ToString() ?? "unknown",
+    serviceVersion: typeof(Program).Assembly.GetName().Version?.ToString() ?? "unknown",
     serviceInstanceId: Environment.MachineName);
 
+// Create a service to expose ActivitySource, and Metric Instruments
+// for manual instrumentation
+appBuilder.Services.AddSingleton<Instrumentation>();
+
 // Configure OpenTelemetry tracing & metrics with auto-start using the
 // StartWithHost extension from OpenTelemetry.Extensions.Hosting.
 appBuilder.Services.AddOpenTelemetry()
@@ -48,7 +52,9 @@ appBuilder.Services.AddOpenTelemetry()
     {
         // Tracing
 
+        // Ensure the TracerProvider subscribes to any custom ActivitySources.
         builder
+            .AddSource(Instrumentation.ActivitySourceName)
             .SetSampler(new AlwaysOnSampler())
             .AddHttpClientInstrumentation()
             .AddAspNetCoreInstrumentation();
@@ -98,7 +104,9 @@ appBuilder.Services.AddOpenTelemetry()
     {
         // Metrics
 
+        // Ensure the MeterProvider subscribes to any custom Meters.
         builder
+            .AddMeter(Instrumentation.MeterName)
             .AddRuntimeInstrumentation()
             .AddHttpClientInstrumentation()
             .AddAspNetCoreInstrumentation();