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