CDK 2.15.0: Cannot get response field from custom resource

[manosntoulias]

Using cdk 2.15.0 I'am trying to create a lambda backed custom resource and get a field from its response but I get the following error:

CustomResource attribute error: Vendor response doesn't contain info.current key in object arn:aws:cloudformation:eu-west-1:238091120948:stack/First/25356620-b1bb-11ec-b3e5-0299088d230d|DemoCustomResourceDemo0225F457|9f3
a0e9b-52f9-45ab-9cba-0823e5a4301b in S3 bucket cloudformation-custom-resource-storage-euwest1. Rollback requested by user.

I thought that the keys in the response of the lambda function must match the string parameter of custom_resource::.get_response_field which in that case would be "info.current". Am I wrong? Here is my code which is simplified and still produces the error. Feel free to replicate this:

Note: There are some commented stuff that I am testing about the response being too large and utilizing the output_paths parameter which is also not working, but let's focus on my questions first.

from aws_cdk.aws_logs import RetentionDays
from constructs import Construct
from aws_cdk import (Stack,
                     aws_iam as iam,
                     aws_lambda as l,
                     CfnOutput,
                     Duration,
                     custom_resources as cr
                     )


class DemoConstruct(Construct):

    def __init__(self, construct: Construct, construct_id: str):
        super().__init__(construct, construct_id)
        with open(f"./resources/lambdas/pathsLambda.py") as lambda_path:
            code = lambda_path.read()
        demo_lambda_function = l.Function(
            scope=self,
            id=f"DemoLambda-{construct_id}",
            code=l.Code.from_inline(code),
            environment={
                "SOME_ARG": "argVal"
            },
            handler="index.lambda_handler",
            runtime=l.Runtime.PYTHON_3_7,
            timeout=Duration.seconds(60),
            memory_size=2048
        )
        c_resource = cr.AwsCustomResource(
            self,
            f"CustomResource-{construct_id}",
            log_retention=RetentionDays.ONE_WEEK,
            on_update=cr.AwsSdkCall(
                service="Lambda",
                action="invoke",
                physical_resource_id=cr.PhysicalResourceId.of("Trigger"),
                parameters={
                    "FunctionName": demo_lambda_function.function_name,
                    "InvocationType": "RequestResponse",
                    "Payload": "{\"Request\":{\"Method\": \"method1\"}}"
                },
                # output_paths=["info.current"]
            ),
            policy=cr.AwsCustomResourcePolicy.from_statements([
                iam.PolicyStatement(
                    actions=["lambda:InvokeFunction"],
                    resources=[demo_lambda_function.function_arn]
                )
            ])
        )
        CfnOutput(self, id="InfoCurrent", value=c_resource.get_response_field("info.current"), export_name="InfoCurrent")


class Demo(Stack):
    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)
        DemoConstruct(self, "Demo")

And the lambda code:

def lambda_handler(event, context):

    print(event)
    print(context)

    myStr = "q"
    #for i in range(4096):
    #    myStr += 'q'
    my_dict = {
        "info": {
            "current": {
                    "version": 3
            },
            "applied": {
                "count": 23
            }
        },
        "other": myStr
    }
    print(my_dict)
    return my_dict

[peterwoodworth]

Hey @manosntoulias,

The output_paths parameter and getResponseField method both work with the Api response.
For example, this custom resource is using the S3 listobjectsv2 API call. If we take a look at that call's response syntax, we can see how the response data will be returned. In this case, the example wants to only return the data seen in the first two objects in Contents, which is an array of Objects.

So for your case, you're using Lambda Invoke. I'm not too sure what info.current is, but it's not in any of the response elements seen here 🙂

Hope this helps guide you in the right direction!

[github-actions[bot]]

Hello! Reopening this discussion to make it searchable.