Allow for a dynamic LambdaS3Code key property

[rclark]

We have CI systems that build lambda code bundles for our applications on commit. These systems write bundles to S3 locations like this:

s3://some-bucket/bundles/application-name/commit-sha.zip

Our CloudFormation templates all have a GitSha parameter that indicates which commit of the application you want to deploy. So when we define Lambda function's now, the code Property is an object that looks like this:

{
  "S3Bucket": "some-bucket",
  "S3Key": { "Fn::Sub": "bundles/application-name/${GitSha}.zip" }
}

I can't seem to reproduce this behavior through the LambdaS3Code construct, which will only accept a string for the key argument.

new Lambda(this, "Function", {
  code: new LambdaS3Code(utilityBucket, new FnSub('bundles/aws-cdk-explorer/${GitSha}.zip')),
  handler: 'index.js',
  runtime: LambdaRuntime.NodeJS
})

[rix0rrr]

Yes, this is not great, and something we're aware of (but unsure how to fix short of introducing a more complex type system involving generics). Before we start making changes, we want to make an inventory of how often these kinds of scenarios occur in practice.

As a workaround, you can bypass the typechecker by putting as any after the value. It will ultimately synthesize to the correct CloudFormation.

[rclark]

we want to make an inventory of how often these kinds of scenarios occur in practice.

I can close this ticket with the as any workaround, unless you want it to hang around for the inventory. Thanks!

[rix0rrr]

Yep, we'll close it, we have the link in the other ticket. Thanks for reporting!