Reel · Chaos & Reliability · Oct 22, 2026
Chaos 101, ep 01: what is a blast radius?
In short
Blast radius is how much breaks when one thing fails. In July 2024, one faulty CrowdStrike update crashed about 8.5 million Windows devices, per Microsoft. Airlines, banks and hospitals went down because one file went to everyone at once. How to shrink it: roll out to 1%, then 10%, then everyone; split users into cells; and make every change easy to stop.
Checklist: what to do about it
- For your next change, write down who is affected if it goes wrong.
- Roll out in stages: 1%, then 10%, then everyone, with a pause to watch in between.
- Define what "stop" looks like before you start, and who can call it.
- Make every change easy to stop: feature flags, kill switches, fast rollback.
- Split users or tenants into cells so one bad cell doesn't take everyone down.
- Don't push config or content to every machine at once either. It needs staging too.