CDK custom resource response for flyway lambda

Question

I have taken a Flyway lambda from this repo and I am trying to implement a custom resource that invokes the lambda whenever the migration source folder changes. It works fine but occasionally the response object exceeds the 4096 byte limit and the stack fails to deploy. Below is my custom resource code:

flyway_resource = cr.AwsCustomResource(
        self,
        f"FlywayCustomResource-{construct_id}",
        log_retention=RetentionDays.ONE_WEEK,
        on_update=cr.AwsSdkCall(
            service="Lambda",
            action="invoke",
            physical_resource_id=cr.PhysicalResourceId.of("FlywayTrigger"),
            parameters={
                "FunctionName": flyway_lambda_function.function_name,
                "InvocationType": "RequestResponse",
                "Payload": "{" +
                           "\"flywayRequest\":{\"flywayMethod\": \"migrate\"}," +
                           " \"assetHash\": \"" +
                           # The hash of this asset (i.e., the local migration folder) changes when the content
                           # of the folder changes and hence an UPDATED life cycle message is produced.
                           # (i.e., the params of the function have changed)
                           assets.Asset(self, "hashId", path=migrations_source).asset_hash +
                           "\"}"
            },
            # This would avoid lambda telling output size too big when erroring, we must use the right selector(s)
            # output_paths=['info', 'errorMessage', 'errorType']
        ),
        policy=cr.AwsCustomResourcePolicy.from_statements([
            iam.PolicyStatement(
                actions=["lambda:InvokeFunction"],
                resources=[flyway_lambda_function.function_arn]
            )
        ])
    )

I know that I can use the output_paths parameter to limit the fields in the response that will be actually selected, but I am not quite sure I have the correct field names in the list. Here's a successful example response of the lambda:

For failure I have names such as 'errorMessage', 'errorType' in the root level (the same level that 'info' exists). I have two questions:

Is the commented output_paths parameter correct? I want to verify that the values of this parameter must match the keys in the json response of the lambda. I have a hard time understanding this in the docs. (If I uncomment it works but it might be because the the specified paths don't exist and the response becomes empty and hence does not exceed the limit anymore)
Assuming that 1) is correct how do I verify the response of the custom resource. In the case that the response in erroneous I would like for the deployment to fail. I know that I can do cr.get_response_field so with cr.get_response_field('info') or cr.get_response_field('errorMessage') perhaps I could check which of these keys exists in another lambda backed custom resource. Is there a better way?

CDK custom resource response for flyway lambda

0 Answers