Kubernetes container connection to RDS instance in separate VPC
With the help of Kelsey Hightower, I solved the problem. It turns out it was a Docker routing issue. I've written up the details in a blog post, but the bottom line is to alter the minions' routing table like so:
$ sudo iptables -t nat -I POSTROUTING -d <RDS-IP-ADDRESS>/32 -o eth0 -j MASQUERADE
Did you modify the source/destination checks as well?
Since your instance will be sending and receiving traffic for IPs other than the one assigned by your subnet, you'll need to disable source/destination checks.
See the image:https://coreos.com/assets/images/media/aws-src-dst-check.png