Comment by toredash

Totally agree!

This service is published more as a concept to be built on top of, than a complete solution.

You wouldn't even need IAM rights to read RDS information, you need subnet information. As subnets are zonal, it does not if the service is RDS or Redis/ElastiCache. The IP returned from the hostname lookup, at the time your pod is scheduled, determines which AZ that Pod should (optimally) be deployed to.

Where this solution was created, was in a multi AWS account environment. Doing describe subnets API calls across multiple accounts is a hassle. It was "good enough" to have a static mapping of subnets, as they didn't change frequently.