fix(telemetry): preserve built-in meter discovery

docs/diagnostics/metrics.md

@@ -4,6 +4,8 @@ TrogonEventStore collects metrics in [Prometheus format](https://prometheus.io/d
 
 In addition, TrogonEventStore can actively export metrics to a specified endpoint using the [OpenTelemetry Protocol](https://opentelemetry.io/docs/specs/otel/protocol/) (OTLP).
 
+The built-in Core and Projections meter sources are always registered. Use the `Meters` array in `metricsconfig.json` only when additional components expose their own `System.Diagnostics.Metrics` meter sources.
+
 ## Metrics reference
 
 ### Caches

src/EventStore.ClusterNode/metricsconfig.json

@@ -8,10 +8,7 @@
 		"Enabled": false
 	},
 
-	"Meters": [
-		"EventStore.Core",
-		"EventStore.Projections.Core"
-	],
+	"Meters": [],
 
 	"Statuses": {
 		"Index": true,

src/EventStore.Core.XUnit.Tests/OpenTelemetry/TelemetryMeterFactoryTests.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Reflection;
 using EventStore.Core.Diagnostics;
 using FluentAssertions;
 using Xunit;
@@ -9,15 +8,12 @@ namespace EventStore.Core.XUnit.Tests.OpenTelemetry;
 public class TelemetryMeterFactoryTests
 {
 	[Fact]
-	public void UsesTheCurrentServerVersionForTheInstrumentationScope()
+	public void UsesTheCurrentInstrumentationVersionForTheScope()
 	{
 		using var meter = TelemetryMeterFactory.Create("test-scope");
-		var informationalVersion = typeof(TelemetryMeterFactory).Assembly
-			.GetCustomAttribute<AssemblyInformationalVersionAttribute>()!
-			.InformationalVersion;
 
 		meter.Name.Should().Be("test-scope");
-		meter.Version.Should().Be(informationalVersion.Split('+', 2)[0]);
+		meter.Version.Should().Be(TelemetryMeterInstrumentation.ScopeVersion);
 	}
 
 	[Theory]

src/EventStore.Core.XUnit.Tests/OpenTelemetry/TelemetryMeterInstrumentationTests.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Reflection;
+using EventStore.Core.Diagnostics;
+using FluentAssertions;
+using Xunit;
+
+namespace EventStore.Core.XUnit.Tests.OpenTelemetry;
+
+public class TelemetryMeterInstrumentationTests
+{
+	[Fact]
+	public void PreservesBuiltInMeterNames()
+	{
+		TelemetryMeterInstrumentation.CoreName.Should().Be("EventStore.Core");
+		TelemetryMeterInstrumentation.ProjectionsName.Should().Be("EventStore.Projections.Core");
+	}
+
+	[Fact]
+	public void UsesTheEmbeddedAssemblyVersionForTheScope()
+	{
+		var informationalVersion = typeof(TelemetryMeterInstrumentation).Assembly
+			.GetCustomAttribute<AssemblyInformationalVersionAttribute>()!
+			.InformationalVersion;
+
+		TelemetryMeterInstrumentation.ScopeVersion.Should().Be(informationalVersion.Split('+', 2)[0]);
+	}
+
+	[Fact]
+	public void IncludesBuiltInMetersOnceBeforeAdditionalMeters()
+	{
+		var names = TelemetryMeterInstrumentation.GetNames([
+			TelemetryMeterInstrumentation.CoreName,
+			"Custom.Component",
+		]);
+
+		names.Should().Equal(
+			TelemetryMeterInstrumentation.CoreName,
+			TelemetryMeterInstrumentation.ProjectionsName,
+			"Custom.Component");
+	}
+
+	[Fact]
+	public void RejectsMissingAdditionalMeterCollection()
+	{
+		var action = () => TelemetryMeterInstrumentation.GetNames(null!);
+
+		action.Should().Throw<ArgumentNullException>();
+	}
+
+	[Theory]
+	[InlineData(null)]
+	[InlineData("")]
+	[InlineData(" ")]
+	public void RejectsInvalidAdditionalMeterNames(string meterName)
+	{
+		var action = () => TelemetryMeterInstrumentation.GetNames([meterName]);
+
+		action.Should().Throw<ArgumentException>();
+	}
+}

src/EventStore.Core/ClusterVNodeStartup.cs

@@ -301,7 +301,7 @@ private static void ConfigureMetrics(
 	{
 		meterOptions
 			.SetResourceBuilder(serviceIdentity.CreateResourceBuilder())
-			.AddMeter(metricsConfiguration.Meters)
+			.AddMeter(TelemetryMeterInstrumentation.GetNames(metricsConfiguration.Meters))
 			.AddView(i =>
 			{
 				if (i.Name == MetricsBootstrapper.LogicalChunkReadDistributionName)

src/EventStore.Core/Diagnostics/TelemetryMeterFactory.cs

@@ -1,29 +1,13 @@
 using System;
 using System.Diagnostics.Metrics;
-using System.Reflection;
 
 namespace EventStore.Core.Diagnostics;
 
 public static class TelemetryMeterFactory
 {
-	private static readonly string InstrumentationScopeVersion = GetInstrumentationScopeVersion();
-
 	public static Meter Create(string instrumentationScopeName)
 	{
 		ArgumentException.ThrowIfNullOrWhiteSpace(instrumentationScopeName);
-		return new Meter(instrumentationScopeName, InstrumentationScopeVersion);
-	}
-
-	private static string GetInstrumentationScopeVersion()
-	{
-		var informationalVersion = typeof(TelemetryMeterFactory).Assembly
-			.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?
-			.InformationalVersion;
-		if (string.IsNullOrWhiteSpace(informationalVersion))
-		{
-			throw new InvalidOperationException("The telemetry assembly has no informational version.");
-		}
-
-		return informationalVersion.Split('+', 2)[0];
+		return new Meter(instrumentationScopeName, TelemetryMeterInstrumentation.ScopeVersion);
 	}
 }

src/EventStore.Core/Diagnostics/TelemetryMeterInstrumentation.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+
+namespace EventStore.Core.Diagnostics;
+
+public static class TelemetryMeterInstrumentation
+{
+	public const string CoreName = "EventStore.Core";
+	public const string ProjectionsName = "EventStore.Projections.Core";
+
+	public static string ScopeVersion { get; } = GetScopeVersion();
+
+	public static string[] GetNames(IEnumerable<string> additionalMeterNames)
+	{
+		ArgumentNullException.ThrowIfNull(additionalMeterNames);
+
+		var names = new List<string> { CoreName, ProjectionsName };
+		var seen = new HashSet<string>(names, StringComparer.Ordinal);
+
+		foreach (var name in additionalMeterNames)
+		{
+			ArgumentException.ThrowIfNullOrWhiteSpace(name);
+			if (seen.Add(name))
+			{
+				names.Add(name);
+			}
+		}
+
+		return names.ToArray();
+	}
+
+	private static string GetScopeVersion()
+	{
+		var informationalVersion = typeof(TelemetryMeterInstrumentation).Assembly
+			.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?
+			.InformationalVersion;
+		if (string.IsNullOrWhiteSpace(informationalVersion))
+		{
+			throw new InvalidOperationException("The telemetry assembly has no informational version.");
+		}
+
+		return informationalVersion.Split('+', 2)[0];
+	}
+}

src/EventStore.Core/MetricsBootstrapper.cs

@@ -84,7 +84,7 @@ public static void Bootstrap(
 			return;
 		}
 
-		var coreMeter = TelemetryMeterFactory.Create("EventStore.Core");
+		var coreMeter = TelemetryMeterFactory.Create(TelemetryMeterInstrumentation.CoreName);
 		var statusMetric = new StatusMetric(coreMeter, "eventstore-statuses");
 		var grpcMethodMetric = new DurationMetric(coreMeter, "eventstore-grpc-method-duration");
 		var gossipLatencyMetric = new DurationMetric(coreMeter, "eventstore-gossip-latency");

src/EventStore.Projections.Core/ProjectionsSubsystem.cs

@@ -205,7 +205,7 @@ private void ConfigureProjectionMetrics(bool isEnabled)
 			return;
 		}
 
-		var projectionMeter = TelemetryMeterFactory.Create("EventStore.Projections.Core");
+		var projectionMeter = TelemetryMeterFactory.Create(TelemetryMeterInstrumentation.ProjectionsName);
 
 		var tracker = new ProjectionTracker();
 		_projectionTracker = tracker;