Problem with auto-naming of singleton lambda functions

[reidca]

The Question

When creating a Singleton Lambda function (https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_aws-lambda.SingletonFunction.html) and not specifying the FunctionName property specifically, CDK creates a name in the format "StackName-SingletonLambdaGUID"

e.g. S3FtpStack-SingletonLambda0d11343f709a4e728c0caf32-XRCK830I30HY

If you have multiple singleton lambda functions this makes it impossible to work out what the function does since they look identical apart from the guid at the end.

I would have expected CDK to use the resource name provided to stem the function name just like it does when creating a lambda.Function.

e.g. S3FtpStack-ftpUploaderHandler6825122D-1LK6V6JG68LPJ

I do not want to name the function specifically because this then makes it impossible for cloudformation to replace the function.

Is this expected behaviour? If so why and could it be changed?

Environment

• CDK CLI Version: 1.15.0 (build bdbe3aa)
• Module Version: 1.11.0",
• OS: All
• Language: TypeScript

[cmckni3]

I have the same issue with logical id generation in general. I set a description on singleton lambda to help me identify them.

I cleaned up logical ids by overriding allocateLogicalId.

I understand the reasoning behind the unique id generation and logical id stability. It makes it difficult to identity resources (especially in nested stacks). It seems to have been discussed before in #1424 and #1594.

I would appreciate guidance from the CDK team as well.

[reidca]

Reading the docs it seems you should be able to override the logical id generation however this doesn't work in my tests.

let baseCfnFunction = myFunction.node.defaultChild as lambda.CfnFunction
baseCfnFunction .overrideLogicalId("mylambdaname")

When I use this code on a lambda.SingletonFunction I get a runtime undefined error:

Cannot read property 'overrideLogicalId' of undefined
Subprocess exited with error 1

[cmckni3]

I ran into the same issue. The method definitely exists on CfnElement still.

renameLogicalId may work.

EDIT Looks like defaultChild is not set for some reason.

[cmckni3]

#207 (comment)

[nija-at]

@reidca & @cmckni3 - we have an option for this called lambdaPurpose as part of SingletonFunction.

Have you tried using that?

[cmckni3]

@nija-at yes, I figured that out.

Is it possible to override purpose on CDK provided custom resources?

[reidca]

@reidca & @cmckni3 - we have an option for this called lambdaPurpose as part of SingletonFunction.

Have you tried using that?

Can I understand why the Lambda.SingletonFunction is different from the Lambda.Function in the way they are named by CDK?

[nija-at]

The SingletonFunction lets you add this function into your stack any number of times and guarantees that it will be added only once, as long as the uuid and the lambdaPurpose remain the same.

This allows for another construct to define a lambda function as part of its construction (using SingletonFunction) such that this other construct can be added to the stack any number of times while guaranteeing that the lambda function is added only once. For example, the GlobalTableCoordinator construct can be added to your stack any number of times but there will be one and only one of the underlying lambda function in the stack.

On the other hand, the regular Function construct will fail with the error that the function already exists in the stack.

Hope that makes sense?

Closing this issue for now. Please reopen if there's something I've missed.