VPC Peering Network debugging

Today I was chasing down a bug where a database that was in a peered VPC couldn’t be connected to. It was a good reminder of the things that should be checked when trying to debug networking issues in AWS.

1. Security groups (in my case the problem was the SG on the database though I checked that after everything else)
2. NACLs
3. Route tables
4. Make sure you can resolve DNS between the paired VPCs

AWS advice on the matter at the time of writting it mentions everything I do minus security groups