How do you deal with the 10+ second cold start times for Lambda when using it in a VPC? Are you pre-warming your lambda functions? Did you open up your RDS instance to the world so you could connect to it from a public lambda network? I know you had to pull some magic, because I've been down that road.
It's been a problem for years and there's been no sign of a solution. Example article from last month: https://medium.freecodecamp.org/lambda-vpc-cold-starts-a-lat...
These are the sorts of problems that turn people off from using serverless architectures.