(Hotswap): CDK v2 Hotswapping support for SAM.CfnFunction

[KingOfPoptart]

Describe the feature

Currently it looks like the only way hotswap will support a lambda is if it is of resource type AWS::Lambda::Function -

aws-cdk/packages/aws-cdk/lib/api/hotswap/lambda-functions.ts

Line 92 in 5024021

if (newResourceType !== 'AWS::Lambda::Function') {

Use Case

We currently use SAM.CfnFunction since it gets us gradual deployments of our lambdas.

We don't want to lose our ability to do gradual deployments with lambda,. As such we're stuck choosing between hot swapping or gradual deployments in the current state of CDK v2.

Proposed Solution

Add support for AWS::Serverless::Function for hot swapping.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

2.20.0

Environment details (OS name and version, etc.)

MacOS 12.3.1

[KingOfPoptart]

I spoke with Rico briefly, and this might be a "not possible"

"Why hotswapping won't work: we can't look into the transform, and so we don't know what a SAM::Function turns into, so we can't call UpdateFunction for you"

I'll leave it open in case anybody else has any clever ideas.

[skinny85]

I actually think it could be doable, because the logical ID of AWS::Serverless::Function will be the same for the AWS::Lambda::Function generated after the transform has executed. You can verify that by using the "View processed template" in the CloudFormation AWS Console in the "Template" tab of a Stack view for any Stack that uses the Serverless transform. And if we have the logical ID, we can get the Lambda's physical name from the CloudFormation API (ListStackResources).