4.2 - Cost-optimized storage (S3 tiers and lifecycle)
AWS Solutions Architect Associate objective 4.2 covers optimising storage cost. When objects are rarely accessed after 30 days but must stay instantly retrievable, an S3 Lifecycle rule that transitions them to S3 Standard-Infrequent Access (Standard-IA) cuts cost while keeping millisecond access. For data that can be regenerated at any time and does not need multi-AZ resilience, such as thumbnails, S3 One Zone-Infrequent Access stores it in a single AZ at lower cost. For archival, Glacier tiers are cheapest with slower retrieval. When an on-premises app needs low-latency local access to frequently used files that are backed by S3, AWS Storage Gateway (File Gateway) caches hot data locally while storing everything in S3. Expect scenario questions that describe access frequency, regenerable data, archival, or hybrid file caching, and ask which S3 tier, lifecycle rule or gateway minimises cost.
Rare access but instant retrieval = S3 Standard-IA (via a Lifecycle rule). Regenerable, no multi-AZ need = S3 One Zone-IA. Cheapest archive, slow retrieval = Glacier. On-prem low-latency files backed by S3 = Storage Gateway (File Gateway).
Practice questions
1. Objects are rarely accessed after 30 days but must stay instantly retrievable. Which automated approach cuts storage cost?
- An S3 Lifecycle rule transitioning to S3 Standard-IA (correct answer)
- Deleting the objects permanently after exactly 30 days
- Enabling S3 Transfer Acceleration on the bucket
- Copying objects to attached EBS volumes
A lifecycle rule can transition objects to S3 Standard-IA (cheaper storage, small retrieval fee) after 30 days while keeping instant access. Deleting loses data; the others do not cut storage cost.
2. A team wants automatic cost savings for S3 data with unknown and changing access patterns, without retrieval fees for moving between frequent and infrequent tiers. Which storage class fits?
- S3 One Zone-IA
- S3 Intelligent-Tiering (correct answer)
- S3 Glacier Deep Archive
- S3 Standard
S3 Intelligent-Tiering moves objects between frequent and infrequent access tiers automatically based on usage, with no retrieval fees for those tiers, ideal for unpredictable access. A small monitoring fee applies per object.
3. An architecture sends large volumes of data from EC2 in one Region to the internet. Which change most directly reduces data transfer cost for repeat content?
- Move all the instances to a much larger instance size
- Enable EBS-optimized throughput on the instances
- Serve repeated content through Amazon CloudFront (correct answer)
- Add a second NAT gateway in another AZ
Serving repeat content via CloudFront caches it at the edge, so most requests are answered from cache and data-out from EC2/S3 to the internet drops, lowering transfer cost. Bigger instances or NAT gateways do not cut egress.
4. Serving images from S3 to a global audience incurs high S3 data-transfer-out costs on repeat requests. What reduces this cost most?
- Enable versioning on the bucket
- Switch the bucket to One Zone-IA
- Put CloudFront in front of the bucket (correct answer)
- Replicate the bucket across more Regions
CloudFront caches objects at edge locations, so repeat requests are served from cache; data transfer from S3 to CloudFront is free, and CloudFront egress is typically cheaper, cutting overall cost. Versioning and replication add cost.
5. A workload runs 24/7 on a fixed instance type and Region for the next three years. Which purchase gives the deepest committed discount?
- On-Demand pricing for maximum flexibility
- Standard Reserved Instances (3-year) (correct answer)
- Spot Instances for the baseline
- Savings Plans limited to one month
A 3-year Standard Reserved Instance for a fixed type/Region gives the deepest discount for steady, unchanging usage. On-Demand has no discount; Spot is interruptible and unsuited to guaranteed always-on baselines.
6. Compliance logs must be retained for seven years, are almost never read, and a retrieval time of several hours is acceptable. Which S3 storage class is cheapest?
- S3 Standard-Infrequent Access for its low per-GB storage price
- S3 Glacier Deep Archive, the lowest-cost class for long-term retention (correct answer)
- S3 One Zone-Infrequent Access to avoid cross-AZ replication cost
- S3 Intelligent-Tiering with the archive access tiers activated
Glacier Deep Archive is the lowest-cost S3 class, designed for data kept years and rarely accessed, with retrieval in hours. It fits long compliance retention where restore latency is acceptable.