AWS is fixing it by moving to IAM authentication in the serverless ecosystem, rather than network segmentation. Serverless Aurora will support IAM auth at scale via its HTTP query protocol.

Keeping Lambda functions warm is great until you have 2 or more requests hitting the function simultaneously. They won't queue behind the pre-warmed function, they will spin up additional Lambda containers to serve in parallel. Unless you don't expect to get concurrent requests, there's no effective way to pre-warm Lambda functions.