November 2, 2025
DNS: Delete ‘N’ Scream
Reproducing the AWS Outage Race Condition with a Model Checker
Dev reenacts AWS outage in a lab, commenters feud: safety lesson or nerd cosplay
TLDR: An engineer simulated the AWS outage’s bug to show how two workers could accidentally delete live DNS records. Comments erupted: fans praise the clarity from formal modeling, pragmatists note real-world trade‑offs, and skeptics say it’s pointless without AWS’s actual code—useful lesson or just lab cosplay?
An engineer rebuilt the recent AWS slip-up in a tiny sandbox, using the Spin model checker to show how two “helpers” could accidentally delete live website records. In plain terms: one robot cleans up while another is still setting the table, and poof—your dinner (DNS entries) disappears. The write-up simplifies AWS’s own post-mortem, focusing on the alleged race between planners and enactors that made records vanish.
But the real fireworks are in the comments. Team Formal Methods is delighted, with one quip imagining “that one guy at AWS” sprinting to model it all in TLA+. Team Pragmatist rolls in to say: cool theory, but real systems are messy—storage budgets, retention windows, and performance hacks mean the “clean” math rarely survives production. Team Skeptic asks the brutal question: without AWS’s actual code, what’s the point—science fair or safety win? Meanwhile, drive-by readers wished for a baby-steps intro and joked that “DNS Enactor” sounds like a Marvel villain, and that this “cleanup” script cleaned a little too hard.
It’s a classic internet split: clarity vs. reality, with spicy side dishes of “explain it like I’m five” and meme-grade snark. And yes, someone compared the race condition to a Mario Kart blue shell—devs never miss a meme.
Key Points
- •The article models a race condition described in an AWS outage post-mortem using the Spin model checker and Promela.
- •A simplified system includes one DNS Planner and two DNS Enactors communicating via Promela channels.
- •Enactors validate plan freshness, apply plans to Route 53, and clean up significantly older plans.
- •A race occurs when one Enactor cleans up while another applies an older plan, leading to deletion of the active plan and simulated DNS failure.
- •Spin explores all process interleavings and checks invariants, producing counterexamples on violations.