Horizontal scaling
Horizontal scaling refers to the process of adding new servers to accommodate your requirements. Workloads are typically divided amongst servers to restrict the number of requests that any single server can handle. Horizontal scaling in cloud computing refers to the process of adding extra instances rather than increasing the size of the existing ones
It entails increasing the number of cluster nodes, lowering the responsibilities of each member node by expanding the keyspace, and adding more end-points for client connections. Horizontal scaling has traditionally been utilized for high-performance computing, applications, and services. Although the capacity of each individual node remains unchanged, the load is reduced due to the spreading of the load across multiple server nodes.Cassandra, MongoDB are good examples of horizontal scaling
Vertical scaling
Vertical scaling refers to the process of adding additional or faster CPUs, memory, or I/O resources to an existing server, or the process of replacing one server with a larger and more capable server. When it comes to vertical scaling in a data center, traditionally, managers accomplished this by purchasing a new, more powerful server and discarding or repurposing the old one. Cloud architects nowadays may achieve vertical scaling by adjusting the size of the instances in their clouds. vertical scaling in cloud computing is possible for everything from ECS instances to RDS databases. Mysql is an example of vertical scaling.
Vertical scaling normally involves a server hardware update. More IOPS (Input/Output Operations), increased CPU/RAM capacity, and increased disc capacity are all reasons to grow vertically. However, even when virtualization is used to provide a better performance, the risk of downtime is significantly larger than when horizontal scalability is used.
Conclusion:
Horizontal scaling is relatively easy to achieve as you can add more machines or instances in the current pool of resources while vertical scaling at the same time can not be done as simply as horizontal because there is always some kind of restriction in the system which cant be avoided.
Sources:
https://dzone.com/articles/vertical-scaling-and-horizontal-scaling-in-aws
https://www.esds.co.in/blog/vertical-scaling-horizontal-scaling/
https://cloudcheckr.com/cloud-automation/horizontal-vertical-cloud-scaling/#:~:text=Horizontal scaling in cloud computing,with a more powerful server.
https://medium.com/@khushalbisht/aws-scaling-horizontally-vs-vertically-3e30e3e71118
