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niranjv/change_lambda_logger_format.py

Last active January 17, 2025 17:32
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Change Python logger format in AWS Lambda
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change_lambda_logger_format.py
# Python logger in AWS Lambda has a preset format. To change the format of the logging statement,
# remove the logging handler & add a new handler with the required format
import logging
import sys
def setup_logging():
logger = logging.getLogger()
for h in logger.handlers:
logger.removeHandler(h)
h = logging.StreamHandler(sys.stdout)
# use whatever format you want here
FORMAT = '%(asctime)s %(message)s'
h.setFormatter(logging.Formatter(FORMAT))
logger.addHandler(h)
logger.setLevel(logging.INFO)
return logger
def lambda_handler(event, context):
logger = setup_logging()
logger.info("This is a test log statement!")
return
# Expected output from Lambda:
#
# START RequestId: 1a2b3c4d-abcd-1234-efgh-1a2b3c4d5e6f Version: $LATEST
# 2017-10-06 22:40:59,653 This is a test log statement!
# END RequestId: 1a2b3c4d-abcd-1234-efgh-1a2b3c4d5e6f
# REPORT RequestId: 1a2b3c4d-abcd-1234-efgh-1a2b3c4d5e6f Duration: 0.41 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 21 MB
@mubeta06
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mubeta06 commented Jul 28, 2022

I prefer keep the number of 3rd party dependencies in my lambdas low but I do like to have control of the logging configuration. I have had some success using something similar to the following:

import logging
import logging.config


config = {
    'version': 1,
    'formatters': {
      'lambda': {
        'class': "logging.Formatter",
        'format': "%(asctime)s %(levelname)s %(aws_request_id)s %(module)s:%(lineno)d %(message)s"
      }
    },
    'filters': {
        'lambda': {
            '()': '__main__.LambdaLoggerFilter'
        }
    },
    'handlers': {
      'lambda': {
        'class': "logging.StreamHandler",
        'level': "DEBUG",
        'formatter': "lambda",
        'filters': ['lambda']
      }
    },
    'loggers': {
      'lambda': {
        'level': "DEBUG",
        'handlers': ["lambda"],
        'propagate': False
      }
    }
}

logging.config.dictConfig(config)

LOG = logging.getLogger('lambda')

def handle(event, context):
    LOG.info('Logging from Lambda with Request ID.')

Obviously this comes with the risk of assuming AWS do not change the runtime bootstrapping code (tested on python3.8 runtime).

@matthewpick
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matthewpick commented Jan 11, 2024

I was able to retain aws_request_id in the log output:
https://gist.github.com/matthewpick/3aa01abfeda36eae717837a99994d3ed

@junah201
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junah201 commented Jan 17, 2025

has anyone managed to find a nice way to get "aws_request_id" when using the approach of removing the default handler and using your own?

Since the default handler's filter injects the aws_request_id into the record, if you remove the default handler, you will not be able to retrieve aws_request_id. Therefore, instead of removing the default handler and adding your own, you should just modify the formatter using setFormatter.

Also you can see the code of default handler and filter
https://github.com/aws/aws-lambda-python-runtime-interface-client/blob/849e874de01776cb386c18fb2c1731d43cd2b2f4/awslambdaric/bootstrap.py#L339C1-L342C20

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