To handle increased load, a team adds more instances of a web app behind a load balancer rather than upgrading to a larger server. What is this called?
A.Vertical scaling (scale up)
Scale up = bigger single server — the scenario adds more instances instead.
B.Horizontal scaling (scale out)
Scale out = more instances in parallel. Correct.
C.Fault tolerance
Fault tolerance is surviving failures — related but not what 'adding instances for load' describes.
D.Geo-distribution
Geo-distribution is placing resources in multiple regions for latency/DR.
Why this answer
Scaling out (horizontal) adds more instances/nodes; scaling up (vertical) makes a single instance more powerful (more CPU/RAM). Adding app instances behind a load balancer is the textbook scale-out pattern.
Correct answer: B · Last reviewed 2026-02-13
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