Log warning on unhandled exception.

awslambdaric/bootstrap.py

@@ -113,6 +113,7 @@ def replace_line_indentation(line, indent_char, new_indent_char):
 
 if _AWS_LAMBDA_LOG_FORMAT == LogFormat.JSON:
     _ERROR_FRAME_TYPE = _JSON_FRAME_TYPES[logging.ERROR]
+    _WARNING_FRAME_TYPE = _JSON_FRAME_TYPES[logging.WARNING]
 
     def log_error(error_result, log_sink):
         error_result = {
@@ -128,6 +129,7 @@ def log_error(error_result, log_sink):
 
 else:
     _ERROR_FRAME_TYPE = _TEXT_FRAME_TYPES[logging.ERROR]
+    _WARNING_FRAME_TYPE = _TEXT_FRAME_TYPES[logging.WARNING]
 
     def log_error(error_result, log_sink):
         error_description = "[ERROR]"
@@ -210,6 +212,9 @@ def handle_event_request(
         )
 
     if error_result is not None:
+        from .lambda_literals import lambda_unhandled_exception_warning_message
+
+        log_sink.log(lambda_unhandled_exception_warning_message, _WARNING_FRAME_TYPE)
         log_error(error_result, log_sink)
         lambda_runtime_client.post_invocation_error(
             invoke_id, to_json(error_result), to_json(xray_fault)

awslambdaric/lambda_literals.py

@@ -0,0 +1,17 @@
+"""
+Copyright 2023 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+"""
+
+lambda_warning = "LAMBDA_WARNING"
+
+# Holds warning message that is emitted when an unhandled exception is raised during function invocation.
+lambda_unhandled_exception_warning_message = str(
+    f"{lambda_warning}: "
+    "Unhandled exception. "
+    "The most likely cause is an issue in the function code. "
+    "However, in rare cases, a Lambda runtime update can cause unexpected function behavior. "
+    "For functions using managed runtimes, runtime updates can be triggered by a function change, or can be applied automatically. "
+    "To determine if the runtime has been updated, check the runtime version in the INIT_START log entry. "
+    "If this error correlates with a change in the runtime version, you may be able to mitigate this error by temporarily rolling back to the previous runtime version. "
+    "For more information, see https://docs.aws.amazon.com/lambda/latest/dg/runtimes-update.html"
+)

awslambdaric/lambda_runtime_client.py

@@ -108,9 +108,11 @@ def post_invocation_result(
     ):
         runtime_client.post_invocation_result(
             invoke_id,
-            result_data
-            if isinstance(result_data, bytes)
-            else result_data.encode("utf-8"),
+            (
+                result_data
+                if isinstance(result_data, bytes)
+                else result_data.encode("utf-8")
+            ),
             content_type,
         )
 

tests/test_bootstrap.py

@@ -20,6 +20,9 @@
 from awslambdaric.lambda_runtime_exception import FaultException
 from awslambdaric.lambda_runtime_log_utils import LogFormat, _get_log_level_from_env_var
 from awslambdaric.lambda_runtime_marshaller import LambdaMarshaller
+from awslambdaric.lambda_literals import (
+    lambda_unhandled_exception_warning_message,
+)
 
 
 class TestUpdateXrayEnv(unittest.TestCase):
@@ -461,7 +464,10 @@ def raise_exception_handler(json_input, lambda_context):
         )
 
         # NOTE: Indentation characters are NO-BREAK SPACE (U+00A0) not SPACE (U+0020)
-        error_logs = "[ERROR] FaultExceptionType: Fault exception msg\r"
+        error_logs = (
+            lambda_unhandled_exception_warning_message
+            + "[ERROR] FaultExceptionType: Fault exception msg\r"
+        )
         error_logs += "Traceback (most recent call last):\r"
         error_logs += '  File "spam.py", line 3, in <module>\r'
         error_logs += "    spam.eggs()\r"
@@ -492,7 +498,10 @@ def raise_exception_handler(json_input, lambda_context):
             0,
             bootstrap.StandardLogSink(),
         )
-        error_logs = "[ERROR] FaultExceptionType: Fault exception msg\rTraceback (most recent call last):\n"
+        error_logs = (
+            lambda_unhandled_exception_warning_message
+            + "[ERROR] FaultExceptionType: Fault exception msg\rTraceback (most recent call last):\n"
+        )
 
         self.assertEqual(mock_stdout.getvalue(), error_logs)
 
@@ -518,7 +527,10 @@ def raise_exception_handler(json_input, lambda_context):
             0,
             bootstrap.StandardLogSink(),
         )
-        error_logs = "[ERROR] FaultExceptionType\rTraceback (most recent call last):\n"
+        error_logs = (
+            lambda_unhandled_exception_warning_message
+            + "[ERROR] FaultExceptionType\rTraceback (most recent call last):\n"
+        )
 
         self.assertEqual(mock_stdout.getvalue(), error_logs)
 
@@ -544,7 +556,10 @@ def raise_exception_handler(json_input, lambda_context):
             0,
             bootstrap.StandardLogSink(),
         )
-        error_logs = "[ERROR] Fault exception msg\rTraceback (most recent call last):\n"
+        error_logs = (
+            lambda_unhandled_exception_warning_message
+            + "[ERROR] Fault exception msg\rTraceback (most recent call last):\n"
+        )
 
         self.assertEqual(mock_stdout.getvalue(), error_logs)
 
@@ -579,8 +594,7 @@ def raise_exception_handler(json_input, lambda_context):
             0,
             bootstrap.StandardLogSink(),
         )
-
-        error_logs = "[ERROR]\r"
+        error_logs = lambda_unhandled_exception_warning_message + "[ERROR]\r"
         error_logs += "Traceback (most recent call last):\r"
         error_logs += '  File "spam.py", line 3, in <module>\r'
         error_logs += "    spam.eggs()\r"
@@ -616,8 +630,10 @@ def test_handle_event_request_fault_exception_logging_syntax_error(
             0,
             bootstrap.StandardLogSink(),
         )
-
-        error_logs = f"[ERROR] Runtime.UserCodeSyntaxError: Syntax error in module 'a': {syntax_error}\r"
+        error_logs = (
+            lambda_unhandled_exception_warning_message
+            + f"[ERROR] Runtime.UserCodeSyntaxError: Syntax error in module 'a': {syntax_error}\r"
+        )
         error_logs += "Traceback (most recent call last):\r"
         error_logs += '  File "<string>" Line 1\r'
         error_logs += "    -\n"