Only logging errors with AWS Lambda

Question

I'm trying to add few lines of code so that, when my AWS Lambda function fails, it logs when it fails and with which input parameters it did. Following the documentation, I added these lines:

logger = logging.getLogger()
logger.setLevel(logging.INFO)
logger.info('user {0}'.format(event["user"]))

They generate some information that are accessible from CloudWatch:

08:50:29 - START RequestId: 92d000ad-b01f-11e8-98a6-c32aa1e3e890 Version: $LATEST
08:50:31 - [INFO] 2018-09-04T08:50:31.781Z 92d000ad-b01f-11e8-98a6-c32aa1e3e890 user xxxxxx
08:50:31 - END RequestId: 92d000ad-b01f-11e8-98a6-c32aa1e3e890
08:50:31 - REPORT RequestId: 92d000ad-b01f-11e8-98a6-c32aa1e3e890 Duration: 2513.04 ms Billed Duration: 2600 ms Memory Size: 896 MB Max Memory Used: 37 MB

However, it seems that every single call of the lambda function creates a log entry in the CloudWatch. As it is, it's impossible to identify the logs associated to failures of the function. Is it instead possible to create log entries only when logging writes the information? In alternative, can an S3 bucket be set to store log files (associated to errors)?

user_8162422 · Answer

Any reason you are not utilizing the log level?

logger.setLevel(logging.ERROR)

If you need to log all events, and Cloudwatch would be a good place to do that, then you could consider creating a metric filter inside Cloudwatch\Logging, to create alerts for all entries having keyword 'error', as an example.

Only logging errors with AWS Lambda

1 Answers