CloudWatch Logs from Lambda

In python, you can create your own logger. When using this logger it will print it to the CloudWatch logs defined in the lambda function.

However, you can set the logging level so it only print out certain logs as configured.

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logger = logging.getLogger()
logger.setLevel(logging.INFO)

def lambda_handler(event, context):
    logger.info("hello world")

This will print “hello world” to the CloudWatch logs.

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logger = logging.getLogger()
logger.setLevel(logging.INFO)

def lambda_handler(event, context):
    logger.info("hello world")
    logger.debug(event)

If I were to add the logger.debug(event) line, it will not print out the event to the CloudWatch logs because the logging level is set to INFO.

But we don’t always want to change the code to change the logging level. We can set the logging level to an environment variable and provide a default to INFO level.

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logger = logging.getLogger()
logger.setLevel(os.environ.get("LOGGING_LEVEL", logging.INFO))

def lambda_handler(event, context):
    logger.info("hello world")
    logger.debug(event)

Now the debug logs will only appear if the LOGGING_LEVEL environment variable is set to DEBUG.

In the Lambda Function configuration, you can set the LOGGING_LEVEL environment variable to DEBUG to see the debug logs.

Remove the environment variable to go back to seeing only the INFO logs.

The logging level can be set to DEBUG or ERROR or CRITICAL or WARNING or INFO.

It is case-sensitive so make sure to use all caps.