feat: Implement DependencyFilterTelemetryProcessor to reduce telemetry volume for successful dependency calls

Author: frasermolyneux

src/XtremeIdiots.Portal.Web/DependencyFilterTelemetryProcessor.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Linq;
+using Microsoft.ApplicationInsights.Channel;
+using Microsoft.ApplicationInsights.DataContracts;
+using Microsoft.ApplicationInsights.Extensibility;
+using Microsoft.Extensions.Configuration;
+
+namespace XtremeIdiots.Portal.Web;
+
+/// <summary>
+/// Filters out successful, fast dependency calls for configured dependency types
+/// to reduce telemetry volume. Failed calls and calls exceeding the duration
+/// threshold are always retained.
+/// </summary>
+public sealed class DependencyFilterTelemetryProcessor : ITelemetryProcessor
+{
+    private readonly ITelemetryProcessor next;
+    private readonly IConfiguration configuration;
+
+    public DependencyFilterTelemetryProcessor(ITelemetryProcessor next, IConfiguration configuration)
+    {
+        ArgumentNullException.ThrowIfNull(next);
+        ArgumentNullException.ThrowIfNull(configuration);
+
+        this.next = next;
+        this.configuration = configuration;
+    }
+
+    public void Process(ITelemetry item)
+    {
+        if (item is DependencyTelemetry dependency && ShouldFilter(dependency))
+            return;
+
+        next.Process(item);
+    }
+
+    private bool ShouldFilter(DependencyTelemetry dependency)
+    {
+        if (string.IsNullOrEmpty(dependency.Type))
+            return false;
+
+        var excludedTypes = configuration["ApplicationInsights:DependencyFilter:ExcludedTypes"]?
+            .Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+        var excludedPrefixes = configuration["ApplicationInsights:DependencyFilter:ExcludedTypePrefixes"]?
+            .Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+
+        var typeMatches =
+            (excludedTypes?.Any(t => string.Equals(dependency.Type, t, StringComparison.OrdinalIgnoreCase)) == true) ||
+            (excludedPrefixes?.Any(p => dependency.Type.StartsWith(p, StringComparison.OrdinalIgnoreCase)) == true);
+
+        if (!typeMatches)
+            return false;
+
+        if (dependency.Success != true)
+            return false;
+
+        var thresholdMs = double.TryParse(
+            configuration["ApplicationInsights:DependencyFilter:DurationThresholdMs"], out var t) ? t : 1000;
+        if (dependency.Duration.TotalMilliseconds > thresholdMs)
+            return false;
+
+        return true;
+    }
+}

src/XtremeIdiots.Portal.Web/Program.cs

@@ -48,6 +48,7 @@
             .Select("GameTracker:*", environmentLabel)
             .Select("Google:*", environmentLabel)
             .Select("FeatureManagement:*", environmentLabel)
+            .Select("ApplicationInsights:*", environmentLabel)
             .ConfigureRefresh(refresh =>
                 refresh.Register("Sentinel", environmentLabel, refreshAll: true)
                        .SetRefreshInterval(TimeSpan.FromMinutes(5)));
@@ -80,6 +81,7 @@
 builder.Services.Configure<TelemetryConfiguration>(telemetryConfiguration =>
 {
     var telemetryProcessorChainBuilder = telemetryConfiguration.DefaultTelemetrySink.TelemetryProcessorChainBuilder;
+    telemetryProcessorChainBuilder.Use(next => new DependencyFilterTelemetryProcessor(next, builder.Configuration));
     telemetryProcessorChainBuilder.UseAdaptiveSampling(
         settings: samplingSettings,
         callback: null,