AWS Lambda universal logging formatter (retain aws_request_id in log output)

aws_logging_util.py

import logging
import os


def setup_logging_format(log_level=logging.INFO, override_existing_loggers=True):
    """
    Logger formatter that works locally and in AWS lambda
    
    :param log_level: Level of logging
    :param override_existing_loggers: Flag for overriding the formatting of all existing loggers
    :return: 
    """
    running_in_aws = os.environ.get("AWS_EXECUTION_ENV") is not None
    delimiter = "\t" if running_in_aws else " "

    log_items = [
        '[%(levelname)s]',
        '[%(asctime)s.%(msecs)dZ]',
        "[%(aws_request_id)s]" if running_in_aws else None,
        '[%(module)s::%(funcName)s:%(lineno)d]',
        '%(message)s'
    ]
    log_format = delimiter.join(filter(None, log_items))
    date_fmt = "%Y-%m-%d %H:%M:%S"

    if running_in_aws:
        log_format += "\n"  # extra new-line expected in AWS

    # Make changes to lambda's default logger (this allows us to retain aws_request_id in log output)
    # https://github.com/aws/aws-lambda-python-runtime-interface-client/blob/2.0.8/awslambdaric/bootstrap.py#L448-L451
    if override_existing_loggers:
        root = logging.getLogger()
        root.setLevel(log_level)
        for handler in root.handlers:
            handler.setFormatter(
                logging.Formatter(
                    fmt=log_format,
                    datefmt=date_fmt,
                )
            )

    logging.basicConfig(
        level=log_level,
        format=log_format,
        datefmt=date_fmt,
    )

lambda_example.py

import json
import logging

from aws_logging_util import setup_logging_format

setup_logging_format()
log = logging.getLogger(__name__)


def lambda_handler(event, _context):
    log.info('processing event: %s', event)
    another_method()
    return {
        'statusCode': 200,
        'event': json.dumps(event)
    }


def another_method():
    log.info('Logging within a method')


if __name__ == '__main__':
    lambda_handler({"test_event": "Test"}, None)

    
# EXAMPLE LOG OUTPUTS:    
# Function Logs
# START RequestId: 7fb639de-3564-4929-9249-dd1d22ef9456 Version: $LATEST
# [INFO]	[2024-01-11 23:12:26.897Z]	[7fb639de-3564-4929-9249-dd1d22ef9456]	[lambda_function::lambda_handler:11]	processing event: {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}
# [INFO]	[2024-01-11 23:12:26.897Z]	[7fb639de-3564-4929-9249-dd1d22ef9456]	[lambda_function::another_method:20]	Logging within a method
# END RequestId: 7fb639de-3564-4929-9249-dd1d22ef9456
# REPORT RequestId: 7fb639de-3564-4929-9249-dd1d22ef9456	Duration: 1.89 ms	Billed Duration: 2 ms	Memory Size: 128 MB	Max Memory Used: 38 MB	Init Duration: 110.48 ms