What is scalability in the cloud?
Scalability is the ability of a system to handle more load by adding resources. In the cloud this is easy because you can add capacity on demand. There are two kinds: vertical scaling means making one machine bigger, and horizontal scaling means adding more machines. Horizontal scaling is usually preferred for large systems.
Two ways to scale
- Vertical scaling: give one server more CPU or memory. Simple but has a hard limit.
- Horizontal scaling: add more servers and share the load between them. Scales much further.
Vertical scaling is easy but you can only make a single machine so big. Horizontal scaling spreads work across many machines, which is how large systems handle millions of users, though it needs a load balancer.
Interviewers like the terms scale up for vertical and scale out for horizontal. Saying you prefer to scale out for large systems because a single machine has limits shows solid understanding.
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