Getting NULL output when running python job

Question

I am running a python job in AWS Lambda to stop ec2 instances based on tags. The script is running properly, but even if the script completes successfully, I am getting output "null" in the result returned by function execution. Attached herewith is the python script. I am new to Python scripting. I am from ops side.

import boto3
import logging

#setup simple logging for INFO
logger = logging.getLogger()
logger.setLevel(logging.INFO)

#define the connection
ec2 = boto3.resource('ec2')

def lambda_handler(event, context):
    # Use the filter() method of the instances collection to retrieve
    # all running EC2 instances.
    filters = [{
            'Name': 'tag:AutoOff',
            'Values': ['True']
        },
        {
            'Name': 'instance-state-name', 
            'Values': ['running']
        }
    ]

    #filter the instances
    instances = ec2.instances.filter(Filters=filters)

    #locate all running instances
    RunningInstances = [instance.id for instance in instances]

    #print the instances for logging purposes
    print RunningInstances 

    #make sure there are actually instances to shut down. 
    if len(RunningInstances) > 0:
        #perform the shutdown
        shuttingDown = ec2.instances.filter(InstanceIds=RunningInstances).stop()
        print shuttingDown
    else:
        print "NOTHING"

I don't see the python script...

Goralight
– Goralight

2017-09-05 08:57:52 +00:00
Commented Sep 5, 2017 at 8:57 — Goralight
– Goralight, Commented Sep 5, 2017 at 8:57
Added the script now..

Pushkar
– Pushkar

2017-09-05 09:00:24 +00:00
Commented Sep 5, 2017 at 9:00 — Pushkar
– Pushkar, Commented Sep 5, 2017 at 9:00

marc_s · Accepted Answer · 2020-01-08 06:23:33Z

1

In order to get response from the lambda you need to return something (usually a dictionary) from lambda_handler method. By default all Python methods return None type, that is why you do not receive any valuable response.

def lambda_handler(event, context):
    ... your code here ...
    return {"turned_off": RunningInstances}

PS. it is preferred to use logging.debug|info|... method instead of print(). You can find more info in the documentation: https://docs.python.org/2.7/library/logging.html

Anyway all the output is saved to CloudWatch Logs. The Log Stream is created automatically when you create a Lambda function. You can find all your prints there for debugging.

edited Jan 8, 2020 at 6:23

marc_s

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answered Sep 5, 2017 at 11:13

Nikolay Grishchenko

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