Explain the difference between vertical and horizontal scaling on AWS.
AWS · Basic level
Answer
Vertical scaling means making one resource bigger; horizontal scaling means adding more resources. Horizontal scaling gives better elasticity and resilience for stateless workloads, while vertical scaling is simpler but limited and may require downtime.
Technical explanation
Horizontal scaling requires externalized state; local sessions or local files break elasticity.
Compute design should balance availability, scaling speed, startup time, instance limits, health checks, and deployment rollback, not just raw instance size.
Autoscaling and load balancing only work well when health checks reflect readiness and when applications externalize state.
Cost optimization should be tied to utilization data and workload tolerance for interruption, commitment, and architecture changes.
Hands-on example
1. Build a launch template or workload definition with IAM role, security groups, user data/bootstrap, health endpoint, and CloudWatch metrics.
2. Place compute behind an ALB/NLB or scaling group and run a controlled load test to observe scaling and health behavior.
3. Tune scaling policy, warmup/cooldown, target group health checks, and rollback procedure.
4. Compare cost and reliability after the test, then promote the configuration through IaC.
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