Casey uses the October 2025 DynamoDB US-East-1 outage as an example of companies publishing shallow "root cause analyses" that explain how symptoms appeared but never show the actual programming bug.
tldr
- •AWS blamed a "race condition" - but that's just the trigger, not the bug
- •the real bug: enactor code crashes hard when it can't read an old/deleted plan for the rollback record
- •that crash should never happen - graceful handling of missing data is basic engineering
- •AWS never showed the actual code (exception? null deref? assertion failure?) - teaches nothing
- •good RCAs (CrowdStrike, Google, Cloudflare) show the actual buggy line - AWS gave none of that depth
what aws said happened
- •DynamoDB endpoints resolved via Route 53 DNS using a constantly-updated "load-balancing tree"
- •single planner generates new tree "plans" (hashed names), three enactors write them to Route 53
- •enactors use distributed lock (via Route 53 atomic ops) so only one updates at a time
- •unlucky enactor gets stuck in long backoff retries, falls way behind (e.g. plan #110 while others on #145+)
- •finally gets lock, writes endpoint to point to ancient plan
- •another enactor sees #110 is stale, garbage-collects it
- •endpoint now points to non-existent DNS name - "no records found"
- •when enactors try to fix it, they also update a "rollback" record pointing to the previous plan
- •previous plan no longer exists - enactor crashes permanently trying to update rollback record
- •all three enactors die the same way - no automatic updates - outage until humans intervene
casey's core criticism
- •everyone calls it a "race condition" and stops thinking
- •race condition is just the trigger that made an old plan get written then deleted
- •real bug: whatever code in the enactor crashes hard when it can't fetch the old plan for the rollback record
- •that crash should never happen:
- rollback field should allow empty/null - stale/missing plan should be gracefully handled (system starts with no prior plan anyway) - operator typo or manual deletion would trigger the exact same total failure - no race needed
- •AWS never explains what the crashing code looked like
- •therefore the RCA teaches nothing useful about avoidable bad programming practices
comparison to better rcas
- •CrowdStrike: buffer overflow from too many rules - clear "don't do that"
- •Google: JSON null-pointer deref - clear lesson
- •Cloudflare: famous one-line bug - they literally showed the line
- •AWS gave none of that depth - leaves engineers suspicious whether they really understood their own bug
bottom line
- •pretending you understand something (or accepting "it was a race condition") is common early in careers
- •real growth comes from refusing to stop until you actually understand the root programming mistake
- •AWS's vague RCA is a textbook example of stopping at the surface instead of showing the real bug