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Cost Optimization & Purchasing
Match commitment to demand: On-Demand, Savings Plans/Reserved, Spot — plus storage tiering.
The purchasing ladder
- On-Demand: unpredictable or short-term; no commitment.
- Savings Plans / Reserved: steady baseline; up to ~72% off for a 1 or 3 year commit.
- Spot: interruptible, fault-tolerant; up to ~90% off.
Storage & data levers
- S3 lifecycle to IA/Glacier; Intelligent-Tiering for unknown patterns.
- Gateway VPC endpoint for S3 to avoid NAT data charges.
- Right-size with utilization data; stop non-prod off-hours.
Tooling
- AWS Budgets for threshold alerts; Cost Explorer for analysis; Compute Optimizer for right-sizing.
Gotchas & exam traps
- Interruptible batch => Spot. Always-on baseline => Savings Plans. Do not commit Reserved to spiky load.
- "Reduce cost of a steady workload" usually = commit + right-size, together.
- Over-provisioned On-Demand at max size is always a wrong answer.
The architect view
Cost optimization is a design decision, not a monthly clean-up. Decide the purchasing and tiering model when you architect, and let automation (lifecycle rules, scaling schedules) keep it honest.