Architecture: Private NAT and Overlapping IP Ranges in AWS

Two teams, two projects, two VPCs. Neither team talked to the other about addressing, so both grabbed the obvious default: 10.0.0.0/16 . Everything worked fine in isolation. Then a business requirement lands: an application in VPC A needs to call a service in VPC B . You reach for VPC peering, and AWS rejects it. You reach for a Transit Gateway, attach both VPCs, and watch one of your routes silently vanish from the route table. The problem is not … Read More

Explained: AWS ENIs (Elastic Network Interfaces)

Your production database server starts throwing errors at 2 a.m. The on-call engineer spins up a replacement instance, and now the scramble begins: update the DNS record, wait for the TTL to expire, reconfigure the firewall rules that were pinned to the old private IP, and hope every downstream service notices the change. Twenty minutes of downtime, most of it spent chasing a network identity that was welded to a machine that no longer exists. Th… Read More