fix(mcp-server): drop noisy HttpClient telemetry metrics (#725)

* fix(mcp-server): drop noisy HttpClient telemetry metrics

Application Insights WorkerService SDK 3.x unconditionally subscribes to
the .NET 8+ built-in 'System.Net.Http' meter with no opt-out via
ApplicationInsightsServiceOptions. ExcelMcp.McpServer makes at most one
lightweight HttpClient call per process (NuGetVersionChecker), so the
connection-pool gauges/histograms were pure noise driving the large
majority of AppMetrics ingestion cost.

Adds OpenTelemetry metric Views (MetricStreamConfiguration.Drop) for the
five noisy http.client.* instruments via ConfigureOpenTelemetryMeterProvider,
which appends to the same MeterProviderBuilder already registered by
AddApplicationInsightsTelemetryWorkerService.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 906eafcb-aa80-4690-83e0-0f98d21fbbe8

* fix(mcp-server): address Copilot review feedback

- Make DroppedHttpClientMetricNames private (only used internally)
- Assert ForceFlush() return value in ProgramTelemetryMetricsTests

---------

Co-authored-by: Stefan Broenner <stbrnner@microsoft.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: 3 people

.changeset/reduce-mcp-telemetry-noise.md

@@ -0,0 +1,5 @@
+---
+"excelmcp": patch
+---
+
+**Reduced MCP Server telemetry noise and cost.** The MCP Server no longer reports the .NET runtime's built-in HTTP-client connection-pool metrics (`http.client.open_connections`, `http.client.active_requests`, `http.client.connection.duration`, `http.client.request.time_in_queue`, `http.client.request.duration`) to Application Insights. These were emitted automatically by the telemetry SDK regardless of actual traffic and accounted for the large majority of telemetry ingestion volume, without providing any useful signal for this tool.

Directory.Packages.props

@@ -23,6 +23,9 @@
     <PackageVersion Include="Microsoft.ApplicationInsights" Version="3.1.2" />
     <PackageVersion Include="OpenTelemetry.Api" Version="1.16.0" />
     <PackageVersion Include="OpenTelemetry.Extensions.Hosting" Version="1.16.0" />
+    <!-- Test-only: verifies dropped-metric View configuration in ExcelMcp.McpServer.Tests -->
+    <PackageVersion Include="OpenTelemetry" Version="1.16.0" />
+    <PackageVersion Include="OpenTelemetry.Exporter.InMemory" Version="1.16.0" />
     <PackageVersion Include="OpenTelemetry.Instrumentation.Http" Version="1.16.0" />
     <PackageVersion Include="OpenTelemetry.Instrumentation.SqlClient" Version="1.16.0" />
     <PackageVersion Include="Azure.Monitor.OpenTelemetry.Exporter" Version="1.8.1" />

src/ExcelMcp.McpServer/Program.cs

@@ -7,6 +7,7 @@
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Console;
+using OpenTelemetry.Metrics;
 using Sbroenne.ExcelMcp.McpServer.Telemetry;
 
 namespace Sbroenne.ExcelMcp.McpServer;
@@ -349,10 +350,45 @@ private static void ConfigureTelemetry(HostApplicationBuilder builder)
 
         builder.Services.AddApplicationInsightsTelemetryWorkerService(aiOptions);
 
+        // AddApplicationInsightsTelemetryWorkerService() unconditionally subscribes to the .NET 8+
+        // built-in "System.Net.Http" meter (via UseApplicationInsightsTelemetry -> AddHttpClientMetrics),
+        // with no opt-out exposed on ApplicationInsightsServiceOptions. ExcelMcp.McpServer makes at most
+        // one lightweight HttpClient call per process (NuGetVersionChecker), so these connection-pool
+        // gauges/histograms are pure noise - they were driving ~96% of billed AppMetrics ingestion.
+        // ConfigureOpenTelemetryMeterProvider appends to the same MeterProviderBuilder already
+        // registered above, so this reliably drops the instruments regardless of registration order.
+        builder.Services.ConfigureOpenTelemetryMeterProvider(ConfigureDroppedHttpClientMetrics);
+
         // Application Insights 3.x no longer exposes the classic telemetry initializer abstraction.
         // ExcelMcpTelemetry enriches each telemetry item with user/session/version context before sending.
     }
 
+    /// <summary>
+    /// Names of the noisy .NET built-in HttpClient meter instruments that ExcelMcp.McpServer never
+    /// consumes. See <see cref="ConfigureTelemetry"/> for why these must be dropped explicitly.
+    /// </summary>
+    private static readonly string[] DroppedHttpClientMetricNames =
+    [
+        "http.client.open_connections",
+        "http.client.active_requests",
+        "http.client.connection.duration",
+        "http.client.request.time_in_queue",
+        "http.client.request.duration",
+    ];
+
+    /// <summary>
+    /// Adds metric Views that drop the noisy HttpClient instruments before export/aggregation.
+    /// Exposed internally (rather than inlined) so it can be exercised directly in unit tests
+    /// without needing a full Application Insights host pipeline.
+    /// </summary>
+    internal static void ConfigureDroppedHttpClientMetrics(MeterProviderBuilder metrics)
+    {
+        foreach (var name in DroppedHttpClientMetricNames)
+        {
+            metrics.AddView(name, MetricStreamConfiguration.Drop);
+        }
+    }
+
     /// <summary>
     /// Registers global exception handlers to capture unhandled exceptions.
     /// </summary>

tests/ExcelMcp.McpServer.Tests/ExcelMcp.McpServer.Tests.csproj

@@ -23,6 +23,9 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <!-- Test-only: verifies OpenTelemetry metric View drop configuration for noisy HttpClient meters -->
+    <PackageReference Include="OpenTelemetry" />
+    <PackageReference Include="OpenTelemetry.Exporter.InMemory" />
     <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>

tests/ExcelMcp.McpServer.Tests/Unit/ProgramTelemetryMetricsTests.cs

@@ -0,0 +1,67 @@
+using System.Diagnostics.Metrics;
+using OpenTelemetry;
+using OpenTelemetry.Metrics;
+using Xunit;
+
+namespace Sbroenne.ExcelMcp.McpServer.Tests.Unit;
+
+/// <summary>
+/// Verifies that the noisy .NET built-in "System.Net.Http" meter instruments
+/// (http.client.open_connections, http.client.active_requests, etc.) are dropped
+/// from the OpenTelemetry metrics pipeline before export.
+///
+/// Background: Microsoft.ApplicationInsights.WorkerService 3.x unconditionally calls
+/// meterProviderBuilder.AddMeter("System.Net.Http") with no opt-out via
+/// ApplicationInsightsServiceOptions. Since ExcelMcp.McpServer makes at most one
+/// lightweight HttpClient call per process (NuGetVersionChecker), these connection-pool
+/// gauges/histograms were driving ~96% of billed Application Insights ingestion.
+/// </summary>
+[Trait("Layer", "McpServer")]
+[Trait("Category", "Unit")]
+[Trait("Feature", "Telemetry")]
+[Trait("Speed", "Fast")]
+public sealed class ProgramTelemetryMetricsTests
+{
+    [Fact]
+    public void ConfigureDroppedHttpClientMetrics_DropsAllNoisyHttpClientInstruments()
+    {
+        using var meter = new Meter(nameof(ConfigureDroppedHttpClientMetrics_DropsAllNoisyHttpClientInstruments));
+
+        var openConnections = meter.CreateUpDownCounter<long>("http.client.open_connections");
+        var activeRequests = meter.CreateUpDownCounter<long>("http.client.active_requests");
+        var requestDuration = meter.CreateHistogram<double>("http.client.request.duration");
+        var connectionDuration = meter.CreateHistogram<double>("http.client.connection.duration");
+        var timeInQueue = meter.CreateHistogram<double>("http.client.request.time_in_queue");
+        var keptMetric = meter.CreateCounter<long>("tool.invocations");
+
+        var exportedMetrics = new List<Metric>();
+
+        var builder = Sdk.CreateMeterProviderBuilder()
+            .AddMeter(meter.Name);
+
+        Program.ConfigureDroppedHttpClientMetrics(builder);
+
+        using var provider = builder
+            .AddInMemoryExporter(exportedMetrics)
+            .Build();
+
+        openConnections.Add(1);
+        activeRequests.Add(1);
+        requestDuration.Record(12.3);
+        connectionDuration.Record(45.6);
+        timeInQueue.Record(7.8);
+        keptMetric.Add(1);
+
+        var flushed = provider.ForceFlush();
+        Assert.True(flushed, "ForceFlush should succeed; a false result would make the metric assertions below misleading.");
+
+        var exportedNames = exportedMetrics.Select(m => m.Name).ToList();
+
+        Assert.DoesNotContain("http.client.open_connections", exportedNames);
+        Assert.DoesNotContain("http.client.active_requests", exportedNames);
+        Assert.DoesNotContain("http.client.request.duration", exportedNames);
+        Assert.DoesNotContain("http.client.connection.duration", exportedNames);
+        Assert.DoesNotContain("http.client.request.time_in_queue", exportedNames);
+        Assert.Contains("tool.invocations", exportedNames);
+    }
+}