Mastering hot upgrades
summary
Klarna’s cred team runs hot upgrades in production for over 20 years using custom upgrade scripts rather than OTP appups; the concrete rules are: keep exported functions for one more release (never remove or change arity used by old code), convert old-format records inside new functions, and split big changes across releases or preload modules carefully. The upgrade pipeline is pre-upgrade (create ETS, start new apps, stop non‑critical workers), upgrade (load modified BEAMs), post‑upgrade (restart services, purge old modules only after no process uses them). Always test upgrades under load and make steps idempotent.
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chapters (5)
- 0:00Introduction
- 2:01How hot upgrades work
- 12:58Building a robust process
- 20:27When to use hot upgrades
- 24:32Questions
