fix: cold start only on on-demand invocation

Author: Attyuttam

powertools-common/src/main/java/software/amazon/lambda/powertools/common/internal/LambdaConstants.java

@@ -28,4 +28,6 @@ private LambdaConstants() {
     public static final String ROOT_EQUALS = "Root=";
     public static final String POWERTOOLS_SERVICE_NAME = "POWERTOOLS_SERVICE_NAME";
     public static final String SERVICE_UNDEFINED = "service_undefined";
+    public static final String AWS_LAMBDA_INITIALIZATION_TYPE = "AWS_LAMBDA_INITIALIZATION_TYPE";
+    public static final String ON_DEMAND_INVOCATION_TYPE = "on-demand";
 }

powertools-common/src/main/java/software/amazon/lambda/powertools/common/internal/LambdaHandlerProcessor.java

@@ -93,7 +93,15 @@ protected static void resetServiceName() {
     }
 
     public static boolean isColdStart() {
-        return isColdStart == null;
+        if (isColdStart != null) {
+            return isColdStart;
+        }
+
+        String initType = System.getenv(LambdaConstants.AWS_LAMBDA_INITIALIZATION_TYPE);
+        boolean cold = LambdaConstants.ON_DEMAND_INVOCATION_TYPE.equals(initType);
+
+        isColdStart = cold;
+        return cold;
     }
 
     public static void coldStartDone() {