Stack Singleton help

[RogerWilco80]

Hi All,

I need some help making a custom-resource.Provider a singleton. I'm kinda beginner at CDK, and Python, so I don't 100% understand classes, constructs, and contexts.

I've done what I think should work, but I don't think it is since it's still creating the onEvent lambda function three times (one for each resource I'm creating), and there aren't a lot of examples out there to reference.

Thank you so much for your help.

Here's what I have so far:

from constructs import Construct
import os
import clone_amis.clone_amis_stack as clone_ami_stack
from aws_cdk import (
    aws_ec2 as ec2,
    custom_resources as cr,
    aws_lambda as lambda_,
    aws_iam as iam,
    aws_logs as logs,
    CustomResource,
    Stack,
    CfnOutput
)

#This Custom Resource makes sure that the AMI's that are required are copied to the right region and shared with the organization.
class CloneShareAMI(Construct):

    def __init__(self, scope: Construct, id: str, *, srcImgId, **kwargs):
        super().__init__(scope, id)

        with open(os.path.join(os.path.dirname(__file__), 'clone_amis/clone_ami_handler.py')) as file:
            code = file.read()

        amiEventHandler = lambda_.Function(
            self,
            id='AMICloneEventHandler',
            runtime=lambda_.Runtime.PYTHON_3_9,
            code=lambda_.Code.from_inline(code),
            handler='index.on_event',
            initial_policy=[
                iam.PolicyStatement(
                    actions=[
                    "ec2:DescribeImageAttribute",
                    "ec2:CopyImage",
                    "ec2:ModifyImageAttribute",
                    "ec2:DescribeImages",
                    "ec2:DerigesterImage",
                    "organizations:DescribeOrganization"
                    ],
                    resources=["*"]
                )
            ]
        )

        amiIsCompleteHandler = lambda_.Function(
            self,
            id='AMICloneIsCompleteHandler',
            runtime=lambda_.Runtime.PYTHON_3_9,
            code=lambda_.Code.from_inline(code),
            handler='index.is_complete',
            initial_policy=[
                iam.PolicyStatement(
                    actions=[
                    "ec2:DescribeImageAttribute",
                    "ec2:ModifyImageAttribute",
                    "ec2:DescribeImages",
                    "ec2:DerigesterImage",
                    "organizations:DescribeOrganization"
                    ],
                    resources=["*"]
                )
            ]
        )

        def get_or_create(scope: Construct):
            stack = Stack.of(scope)
            uniqueid = "awsAMICloneShareProvider"
            existing = stack.node.try_find_child(uniqueid)
            if existing:
                return existing
            return cr.Provider(stack, uniqueid, 
                on_event_handler=amiEventHandler,
                is_complete_handler=amiIsCompleteHandler,
                log_retention=logs.RetentionDays.ONE_DAY
            )

        amiCRProvider = get_or_create(self)
        
        ## Original provider for reverence
        # amiCRProvider = cr.Provider(
        #     self,
        #     "amiProvider",
        #     on_event_handler=amiEventHandler,
        #     is_complete_handler=amiIsCompleteHandler,
        #     log_retention=logs.RetentionDays.ONE_DAY,
        # )

        CustomResource(self, "ami1", 
            service_token=amiCRProvider.service_token,
            properties={"srcImgId" : srcImgId}
        )

and:

from aws_cdk import Stack
import environments as environment
import livn_constructs
from constructs import Construct        

class CloneAMIsStack(Stack):

    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)

        for key, value in environment.AMIs.items():
            livn_constructs.CloneShareAMI(self, f"{key}CloneAMI", srcImgId=value)

[peterwoodworth]

Hey @RogerWilco80,

If my understanding is correct, you only want one provider for all CloneShareAMI you create, instead of one provider for each. is that right?

If so, then you're doing this right for the Provider, and you should only have one provider in your stack. However, you aren't implementing any getOrCreate checks for the Lambda Functions you're defining, so when you instantiate this CloneShareAMI construct three times, those lambda functions will get created three times.

You should either define these Lambda functions outside of this construct, or implement a similar getOrCreate check for these functions within this construct.

[RogerWilco80]

Hi @peterwoodworth,

Thank you for your reply. Sorry for not getting back to you sooner, I was pulled away for another project, but back to this one now.

The bit about defining the Lambda function outside the construct is the bit I was missing, thank you.
Re creating only one provider for all CloneShareAMI, am I right in my understanding that this is the recommended way of implementing custom resources using the custom_resources.Provider?

[peterwoodworth]

Re creating only one provider for all CloneShareAMI, am I right in my understanding that this is the recommended way of implementing custom resources using the custom_resources.Provider?

Yes, that is correct if the handler logic is the same, which it should be 🙂 You should be good to go after adjusting the lambda function creation