Python CustomResource lambda returning null

[RogerWilco80]

Hi All,

I've written a custom resource using python and the custom-resources.Provider, and included an isComplete handler.
I'm finding that when I deploy my stack, the isComplete handler isn't getting the properties I'm returning from the onEvent handler. The CloudWatch logs show that the function is returning null.

CDK version is 2.73.0

Code:

import boto3
import json

ec2=boto3.client('ec2')
ec2Syd=boto3.client('ec2', region_name='ap-southeast-2')
organization=boto3.client('organizations')

def on_event(event, ctx):
    print(event)
    request_type = event['RequestType']
    if request_type == 'Create': return on_create(event)
    if request_type == 'Update': return on_update(event)
    if request_type == 'Delete': return on_delete(event)
    raise Exception("Invalid request type: %s" % request_type)

def on_create(event):
    on_update(event)

def on_update(event):
    props = event['ResourceProperties']
    print("create new resource with props %s" % props)
    
    srcImgId = props['srcImgId']

    srcImgInfo = ec2Syd.describe_images(
        ImageIds=[srcImgId]
    )

    newImg = ec2.copy_image(
        ClientToken=event['RequestId'],
        Description=srcImgInfo['Images'][0]['Description'],
        Encrypted=False,
        Name=srcImgInfo['Images'][0]['Name'],
        SourceImageId=srcImgId,
        SourceRegion='ap-southeast-2',
        CopyImageTags=True
    )
    
    physical_id = newImg['ImageId']
    blkDevices = ec2.describe_images(ImageIds=[newImg['ImageId']])['Images'][0]['BlockDeviceMappings']
    orgInfo = organization.describe_organization()
    returnString = {
        "PhysicalResourceId": physical_id,
        "orgArn": orgInfo['Organization']['Arn'],
        "blkDevices": blkDevices
        }
    return json.dumps(returnString)

def on_delete(event):
    physical_id = event["PhysicalResourceId"]
    print("delete resource %s" % physical_id)

def is_complete(event, context):
    print(event)
    physical_id = event["PhysicalResourceId"]
    orgArn = event['orgArn']
    request_type = event["RequestType"]
    blkDevices = event['blkDevices']
    
    if ec2.describe_images(ImageIds=[physical_id])['Images'][0]['State'] == 'pending':  
        is_ready = False
    else:
        if request_type == 'Delete':
            ec2.deregister_image(ImageId=physical_id)
            for device in blkDevices:
                snapshotId=device['Ebs']['SnapshotId']
                ec2.delete_snapshot(SnapshotId=snapshotId)
        elif request_type == 'Create' or request_type == 'Update':
            ec2.modify_image_attribute(
                Attribute = 'launchPermission',
                ImageId = physical_id,
                OperationType='add',
                OrganizationArns=orgArn
            )
        is_ready = True

    return { "IsComplete": is_ready }

Log event showing null being returned:

2023-04-16T23:34:03.308Z	9140e31a-eec5-4f06-9360-94d1613f0cd2	INFO	[provider-framework] onEvent returned: null

[RogerWilco80]

OMG, I'm such a dope. I realised earlier today that onUpdate is passing back to onCreate (sometimes) then to onEvent and the json object isn't being passed back properly through those.

It's interesting to note (to me anyways) that when using json.dumps() to return the json object, the logs show it being returned properly, but then being split into a key: value pair for each letter with the key being a sequential number, just returning it as normal and it all works properly.

[github-actions[bot]]

Hello! Reopening this discussion to make it searchable.