[Instrumentation.AWSLambda] Incoming FaaS Span attributes: detect and set attribute for cold start

src/OpenTelemetry.Instrumentation.AWSLambda/AWSLambdaWrapper.cs

@@ -18,6 +18,8 @@ public static class AWSLambdaWrapper
 
     private static readonly ActivitySource AWSLambdaActivitySource = new(ActivitySourceName, typeof(AWSLambdaWrapper).Assembly.GetPackageVersion());
 
+    private static bool isColdStart = true;
+
     /// <summary>
     /// Gets or sets a value indicating whether AWS X-Ray propagation should be ignored. Default value is false.
     /// </summary>
@@ -160,7 +162,9 @@ public static Task<TResult> TraceAsync<TInput, TResult>(
             }
         }
 
-        var functionTags = AWSLambdaUtils.GetFunctionTags(input, context);
+        // No parallel invocation of the same lambda handler expected.
+        var functionTags = AWSLambdaUtils.GetFunctionTags(input, context, isColdStart);
+        isColdStart = false;
         var httpTags = AWSLambdaHttpUtils.GetHttpTags(input);
 
         // We assume that functionTags and httpTags have no intersection.
@@ -170,6 +174,9 @@ public static Task<TResult> TraceAsync<TInput, TResult>(
         return activity;
     }
 
+    // Use only for testing.
+    internal static void ResetColdStart() => isColdStart = true;
+
     private static void OnFunctionStop(Activity? activity, TracerProvider? tracerProvider)
     {
         activity?.Stop();

src/OpenTelemetry.Instrumentation.AWSLambda/CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+* Add detection of Lambda cold start and set `faas.coldstart` Activity tag.
+  ([#2037](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/2037))
+
 ## 1.3.0-beta.1
 
 Released 2024-Jan-26

src/OpenTelemetry.Instrumentation.AWSLambda/Implementation/AWSLambdaSemanticConventions.cs

@@ -16,4 +16,5 @@ internal static class AWSLambdaSemanticConventions
     public const string AttributeFaasName = "faas.name";
     public const string AttributeFaasVersion = "faas.version";
     public const string AttributeFaasTrigger = "faas.trigger";
+    public const string AttributeFaasColdStart = "faas.coldstart";
 }

src/OpenTelemetry.Instrumentation.AWSLambda/Implementation/AWSLambdaUtils.cs

@@ -98,11 +98,12 @@ internal static string GetCloudProvider()
         return Environment.GetEnvironmentVariable(FunctionVersion);
     }
 
-    internal static IEnumerable<KeyValuePair<string, object>> GetFunctionTags<TInput>(TInput input, ILambdaContext context)
+    internal static IEnumerable<KeyValuePair<string, object>> GetFunctionTags<TInput>(TInput input, ILambdaContext context, bool isColdStart)
     {
         var tags = new List<KeyValuePair<string, object>>
         {
             new(AWSLambdaSemanticConventions.AttributeFaasTrigger, GetFaasTrigger(input)),
+            new(AWSLambdaSemanticConventions.AttributeFaasColdStart, isColdStart),
         };
 
         var functionName = GetFunctionName(context);

test/OpenTelemetry.Instrumentation.AWSLambda.Tests/AWSLambdaWrapperTests.cs

@@ -213,6 +213,30 @@ public void OnFunctionStart_NoSampledAndAwsXRayContextExtractionDisabled_Activit
         Assert.NotNull(activity);
     }
 
+    [Theory]
+    [InlineData(1)]
+    [InlineData(2)]
+    public void OnFunctionStart_ColdStart_ColdStartTagHasCorrectValue(int invocationsCount)
+    {
+        AWSLambdaWrapper.ResetColdStart();
+        Activity? activity = null;
+
+        using (var tracerProvider = Sdk.CreateTracerProviderBuilder()
+                   .AddAWSLambdaConfigurations(c => c.DisableAwsXRayContextExtraction = true)
+                   .Build())
+        {
+            for (int i = 1; i <= invocationsCount; i++)
+            {
+                activity = AWSLambdaWrapper.OnFunctionStart("test-input", new SampleLambdaContext());
+            }
+        }
+
+        Assert.NotNull(activity);
+        Assert.NotNull(activity.TagObjects);
+        var expectedColdStartValue = invocationsCount == 1 ? true : false;
+        Assert.Contains(activity.TagObjects, x => x.Key == AWSLambdaSemanticConventions.AttributeFaasColdStart && expectedColdStartValue.Equals(x.Value));
+    }
+
     private static ActivityContext CreateParentContext()
     {
         var traceId = ActivityTraceId.CreateFromString(TraceId.AsSpan());