Cost Optimization — AWS Developer (DVA-C02)
Savings Plans and Reserved Instances Commit to Different Scopes
Standard Reserved Instances and Compute Savings Plans both reduce EC2 spend, but they commit you to different axes of flexibility. Reserved Instances give the deepest discount but lock to instance type, region, and OS. Compute Savings Plans apply across instance families and regions at a lower discount percentage. For a workload that is stable in instance type and region over 12 months, the narrower commitment of Standard Reserved Instances produces the larger dollar saving despite the reduced flexibility. Convertible Reserved Instances allow instance family changes during the term at a smaller discount than Standard, trading commitment depth for adaptability.
What This Pattern Tests
The exam presents a running workload and asks you to reduce costs. Spot Instances save 60-90% but require fault tolerance. Savings Plans save 20-40% with 1-year or 3-year commitment to a consistent compute spend (flexible across instance families with Compute Savings Plans). Reserved Instances save similarly but lock to specific instance types and regions. Graviton (ARM) instances offer ~20% better price-performance than x86. The trap is recommending Spot for a latency-sensitive web API (interruptions cause errors) or Reserved Instances for a workload that runs 2 hours per day (break-even requires ~40% utilization).
Decision Axis
Workload characteristics (fault tolerance, utilization pattern, flexibility needs) determine which pricing model applies — not just the discount percentage.
Associated Traps
More Top Traps on This Exam
Decision Rules
Determine that inspecting the S3 storage class of objects under the affected prefix is the one step that causally explains both the cost anomaly (Glacier per-GB retrieval fees) and the latency symptom (Glacier restore delay of minutes to hours), given that inter-region egress has been ruled out.
When S3 cost rises and retrieval latency increases from milliseconds to minutes on the same prefix while egress is ruled out, inspect the storage class of the affected objects — Glacier-tier retrieval fees and restore latency are the only S3 cost category that causally explains both symptoms at once.
Domain Coverage
Difficulty Breakdown