What is the difference between scaling the system by increasing the capacity of a single server and adding additional servers?

The difference between vertical scaling of a single server (vertical scaling) and adding additional servers (horizontal scaling) is as follows:

• Vertical scaling — improving the characteristics of a single server: increasing CPU, memory, disk space. Advantages — simplicity of implementation, does not require changes in the application architecture. Disadvantages — there is a physical limit to capacity, possible downtime during upgrades.

• Horizontal scaling — adding new servers to a cluster, distributing load among them. Advantages — high fault tolerance, scalability almost without limits. Disadvantages — requires support for a distributed architecture, load balancing, and data synchronization.

Example: if you have a web application, vertical scaling will allow processing more requests on a single server, while horizontal scaling will distribute requests among multiple servers, improving fault tolerance and scalability.