Horizontal scaling is splitting the load between different servers.

▪ Simply adds more instances of machines without changing to existing

specifications.

▪ Share the processing power and load balancing across multiple

machines.

▪ Horizontal scaling means adding more machines to the resource pool.

▪ Scaling horizontally gives you scalability but also reliability.

▪ Preferred way to scale in distributed architectures.

▪ When splitting into multiple servers, we need to consider if you have a

state or not.

▪ if we have a state like database servers, than we need to manage more

considerations like CAP theorem. 

https://www.section.io/blog/scaling-horizontally-vs-vertically/