Process of adding more power (CPU, RAM, etc) to the servers
Also referred as “scale up”
Good option when traffic is low
Advantages
Simplicity
Disadvantages
Has a hard limit in terms of the hardware available
Impossible to add unlimited CPU and memory to a single server
No failover and redundancy
If one server goes down, the website/app goes down with it completely
If many users access the web server simultaneously and it reaches the web server’s load limit, users will experience slower response or fail to connect
Overall cost of vertical scaling is high. Powerful servers are much more expensive