99
horizontal scaling
also scale out, not up
More machines, not a bigger one. That only works if no single process owns the user.
What is horizontal scaling?
Vertical scaling buys a larger box. Horizontal scaling adds boxes. Horizontal demands stateless workers, shared data, and a way to route. A bigger box fails as one piece.
Why does horizontal scaling matter when vibe coding?
Models answer “make it scale” with a larger instance type and a comment. The next limit is the same shape, just later. Say scale out and name the shared state.
How do you do horizontal scaling?
List what is in memory: sessions, caches, locks, uploads. Move those out. Then a second instance must pass the same tests. One machine dying must not drop everyone.
How do you ask a model for horizontal scaling?
Scale (service) horizontally. No per-user state in process memory. Two instances must behave the same. Killing one must not lose writes that were acknowledged.
What goes wrong with horizontal scaling?
Ten containers sharing one SQLite file on one disk. You multiplied the app and kept a single data choke.