Backend & systems·Scaling and load management
you add three more identical instances behind the load balancer instead of making the existing one bigger.
Horizontal scaling
Also calledscale out
Adding more machines to spread load. It has no ceiling in principle and gives you redundancy for free, which vertical scaling does not. It requires the work to be partitionable and the instances to be stateless, and it moves your bottleneck to whatever is still shared — usually the database.