Allow AWS Lambda to access RDS Database

Question

I am trying to connect to RDS Database from an AWS Lambda (Java).

Which IP should I enable from the RDS Security group rules?

Answer 1

Here is what I did

I assigned same Subnets and VPCs to both services Lambda and RDS. Now I created a NAT Gateway choosing one of the subnet so that Lambda can use that NAT Gateway to interact with the outside world.

Last thing is to add inbound entry in the security group that is attached to RDS as well as Lambda functions. Whitelist DB port 5432 in my case for postgresql and add security group name in the source.

Security group is somehow whitelisting itself by adding an entry in inbound rules.

This worked for me pretty well.