How would you right-size EC2 and RDS instances to cut spend without hurting reliability?
AWS · Advanced level
Answer
Rightsizing EC2 and RDS means comparing actual CPU, memory, I/O, network, latency, connections, and peak patterns against capacity. I change gradually, test performance, and preserve failover and reliability headroom.
Technical explanation
Average CPU is not enough for rightsizing; p95/p99, memory, I/O, failover headroom, and business peaks matter.
Cost analysis should be based on tagged usage, CUR/Cost Explorer data, service-level owners, and usage-type drivers rather than account-level totals only.
Every cost reduction should be checked against reliability, performance, security, and operational risk.
Use budgets and anomaly detection for early signal, then use rightsizing, lifecycle, commitments, scheduling, and architecture fixes for remediation.
Hands-on example
1. Use Cost Explorer or CUR/Athena to identify the top cost driver by account, service, tag, Region, usage type, and daily delta.
2. Validate the operational cause with service metrics such as utilization, logs volume, NAT bytes, snapshot growth, or data transfer.
3. Apply a targeted fix - rightsizing, lifecycle, retention, endpoint, schedule, or commitment - with a rollback plan.
4. Track savings, performance, and reliability for at least one billing cycle.
Check how well your resume matches the role with our free resume checker— match score, ATS check, and the skills you're missing.
More AWS interview questions
- What is the AWS shared responsibility model, and where is the line between AWS and the customer?
- Explain the difference between a Region, an Availability Zone, and an Edge Location.
- What is a VPC, and what are its core components (subnets, route tables, IGW, NAT)?
- Difference between a public and a private subnet, and how does each reach the internet?
- What is the difference between a Security Group and a Network ACL?
- Are Security Groups stateful or stateless? What about NACLs?
- What is an Internet Gateway versus a NAT Gateway, and when do you need each?
- How does a NAT Gateway differ from a NAT instance?