Layers added to a Function that has no layers in AWS are no longer ignored

templates/hooks/function/sdk_read_one_post_set_output.go.tpl

@@ -39,6 +39,11 @@
 		ko.Spec.Layers = layer
 		ko.Status.LayerStatuses = f16
 	} else {
+		// ko is a deep copy of the desired resource, so Spec.Layers has to be
+		// explicitly cleared when the function has no layers in AWS. Leaving the
+		// desired value in place makes desired and latest identical, no delta is
+		// computed for Spec.Layers and the layers are never attached.
+		ko.Spec.Layers = nil
 		ko.Status.LayerStatuses = nil
 	}
 	if resp.Tags != nil {

test/e2e/resources/function_no_layers.yaml

@@ -0,0 +1,15 @@
+apiVersion: lambda.services.k8s.aws/v1alpha1
+kind: Function
+metadata:
+  name: $FUNCTION_NAME
+  annotations:
+    services.k8s.aws/region: $AWS_REGION
+spec:
+  name: $FUNCTION_NAME
+  code:
+    s3Bucket: $BUCKET_NAME
+    s3Key: $LAMBDA_FILE_NAME
+  role: $LAMBDA_ROLE
+  runtime: python3.9
+  handler: main
+  description: function created by ACK lambda-controller e2e tests

test/e2e/tests/test_function.py

@@ -800,6 +800,78 @@ def test_function_layers(self, lambda_client):
         # Check Lambda function doesn't exist
         assert not lambda_validator.function_exists(resource_name)
 
+    def test_function_add_layers_to_function_without_layers(self, lambda_client):
+        resource_name = random_suffix_name("functionnolayers", 24)
+
+        resources = get_bootstrap_resources()
+        logging.debug(resources)
+
+        replacements = REPLACEMENT_VALUES.copy()
+        replacements["FUNCTION_NAME"] = resource_name
+        replacements["BUCKET_NAME"] = resources.FunctionsBucket.name
+        replacements["LAMBDA_ROLE"] = resources.EICRole.arn
+        replacements["LAMBDA_FILE_NAME"] = LAMBDA_FUNCTION_FILE_ZIP
+        replacements["AWS_REGION"] = get_region()
+
+        # Load Lambda CR that does not declare any layer
+        resource_data = load_lambda_resource(
+            "function_no_layers",
+            additional_replacements=replacements,
+        )
+        logging.debug(resource_data)
+
+        # Create k8s resource
+        ref = k8s.CustomResourceReference(
+            CRD_GROUP, CRD_VERSION, RESOURCE_PLURAL,
+            resource_name, namespace="default",
+        )
+        k8s.create_custom_resource(ref, resource_data)
+        cr = k8s.wait_resource_consumed_by_controller(ref, wait_periods=CONTROLLER_WAIT_PERIODS, period_length=CONTROLLER_PERIOD_LENGTH)
+
+        assert cr is not None
+        assert k8s.get_resource_exists(ref)
+
+        time.sleep(CREATE_WAIT_AFTER_SECONDS)
+
+        cr = k8s.wait_resource_consumed_by_controller(ref, wait_periods=CONTROLLER_WAIT_PERIODS, period_length=CONTROLLER_PERIOD_LENGTH)
+
+        lambda_validator = LambdaValidator(lambda_client)
+
+        # Check Lambda function exists and has no layer attached
+        assert lambda_validator.function_exists(resource_name)
+        function = lambda_validator.get_function(resource_name)
+        assert "Layers" not in function["Configuration"]
+
+        # Add layers to a function that currently has none. GetFunction returns
+        # no layer for it, so the controller has to clear Spec.Layers on the
+        # latest resource for the delta against the desired spec to be computed.
+        layers_list = ["arn:aws:lambda:us-west-2:017000801446:layer:AWSLambdaPowertoolsPythonV2:68", "arn:aws:lambda:us-west-2:580247275435:layer:LambdaInsightsExtension:52"]
+        cr["spec"]["layers"] = layers_list
+
+        # Patch k8s resource
+        k8s.patch_custom_resource(ref, cr)
+        time.sleep(UPDATE_WAIT_AFTER_SECONDS)
+
+        # Check the layers were attached to the function in AWS
+        function = lambda_validator.get_function(resource_name)
+        assert len(function["Configuration"]["Layers"]) == len(layers_list)
+        for i in range(len(layers_list)):
+            assert function["Configuration"]["Layers"][i]["Arn"] == layers_list[i]
+
+        # Check the layers are also reported back in the CR status
+        cr = k8s.get_resource(ref)
+        assert cr["status"]["layerStatuses"] is not None
+        assert len(cr["status"]["layerStatuses"]) == len(layers_list)
+
+        # Delete k8s resource
+        _, deleted = k8s.delete_custom_resource(ref, wait_periods=DELETE_WAIT_PERIODS, period_length=DELETE_PERIOD_LENGTH)
+        assert deleted is True
+
+        time.sleep(DELETE_WAIT_AFTER_SECONDS)
+
+        # Check Lambda function doesn't exist
+        assert not lambda_validator.function_exists(resource_name)
+
     def test_function_event_invoke_config(self, lambda_client):
         resource_name = random_suffix_name("lambda-function", 24)