Cost optimization is not “pick the cheapest service.” It is meeting the required outcome at the lowest total cost, including operations, data transfer, idle capacity, licenses, and recovery risk.
Apply cost levers in a stable order
- Remove idle resources and unnecessary data movement.
- Right-size and enable elasticity.
- Match storage class and retention to access.
- Commit only the steady baseline.
- Use Spot for interruption-tolerant excess work.
- Prefer managed/serverless when reduced operations outweigh unit price.
- Measure with Cost Explorer, Budgets, anomaly detection, tags, and the Cost and Usage Report.
Watch NAT Gateway processing, cross-AZ transfer, cross-Region transfer, public IPv4, idle load balancers, over-retained logs, and frequent retrieval from archival storage. Sometimes a VPC endpoint or CloudFront reduces both cost and latency.
High-frequency pairs
| Do not confuse | Decision |
|---|---|
| Multi-AZ / read replica | Failover / read scaling |
| SG / NACL | Stateful resource / stateless subnet |
| SQS / SNS | Work queue / fan-out |
| Kinesis Streams / Firehose | Retain and process / buffer and deliver |
| CloudWatch / CloudTrail / Config | Operations / API audit / configuration |
| CloudFront / Global Accelerator | HTTP cache / network acceleration |
| Gateway / interface endpoint | S3+DynamoDB route / ENI-based PrivateLink |
| Pilot light / warm standby | Core only / scaled-down full stack |
A practice-question log that improves decisions
Record four fields: decisive phrase, chosen architecture, rejected alternative, and rule to reuse. Revisit errors by rule—for example “availability versus read scale”—rather than by service chapter. When two answers seem correct, locate the requirement one option does not satisfy, then compare operational complexity and cost.
Final lens: the exam rewards explicit trade-offs. “Always use serverless,” “always use Multi-Region,” and other absolutes are usually wrong.
Final checklist
- Can I trace identity, network, data, and failure paths?
- Can I explain why the runner-up answer fails one requirement?
- Do I know which services scale reads, writes, compute, or queues?
- Did I choose recovery scope from RTO/RPO?
- Did I include operations and transfer in the cost?