Definition
Horizontal Scaling
Adding more servers to handle increased load, as opposed to vertical scaling which means upgrading a single server.
Horizontal scaling (scaling out) involves adding more instances of an application behind a load balancer to distribute traffic. This approach allows virtually unlimited growth and provides redundancy — if one server fails, others continue serving requests. However, horizontal scaling requires stateless application design, externalized session storage, shared database access, and proper load balancing. Applications built without these considerations (common in vibecoded projects) cannot scale horizontally without significant rearchitecting.
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