Q23: Keeping Backup Files Forever at the Lowest Possible Cost

Problem Info

Domain	Design Cost-Optimized Architectures
Services	Amazon S3 Standard, S3 Glacier Deep Archive, S3 Lifecycle policies
Difficulty	Easy

Question

Backup files are stored in S3 Standard, accessed frequently for the first month, then never accessed again — but must be kept indefinitely.

Which storage solution meets this most cost-effectively?

Correct Answer

Create an S3 Lifecycle configuration to transition objects from S3 Standard to S3 Glacier Deep Archive after 1 month.

Why this is correct

This question has a clean, known access pattern — frequent for exactly 30 days, then permanently cold — which is precisely what an S3 Lifecycle transition rule is designed to automate.

S3 Glacier Deep Archive is AWS’s lowest-cost storage class, built for data that is rarely (if ever) accessed again and can tolerate a retrieval time measured in hours. Since these backups are described as never accessed after month one, and must be retained indefinitely, Deep Archive’s ultra-low per-GB storage price minimizes long-term cost far more than any “warmer” tier would, and the multi-hour retrieval time is an acceptable trade-off since the files aren’t expected to be pulled back on demand.

Setting a Lifecycle rule to transition objects automatically at the 1-month mark means the files get full-speed S3 Standard access during the period they’re actually needed, then drop to the cheapest possible storage the moment that access pattern ends — with zero manual intervention going forward.

Why the alternatives fall short

• Leave everything in S3 Standard indefinitely — correct for accessibility, but by far the most expensive option for data that’s never touched again after month one — fails “most cost-effective.”
• Transition to S3 Standard-IA after 1 month instead of Glacier Deep Archive — cheaper than Standard, but Standard-IA is priced for data accessed occasionally, not data that’s never accessed again. Since these backups have zero further access, Deep Archive’s much lower storage price wins decisively for a “keep indefinitely, never read again” pattern.
• Delete the files after 1 month to save cost — violates the explicit requirement to keep the files indefinitely; not a valid option regardless of cost.

Exam Tip

When you see a clear, described time-based transition (“accessed frequently for X, then never again, must be kept forever/long-term”), that’s a Lifecycle policy question, and the final tier should match how “cold” the data truly is: rarely accessed but might need it back reasonably fast → Standard-IA/Glacier Instant Retrieval; essentially never accessed again, retention/compliance driven, retrieval-time-tolerant → Glacier Deep Archive, the cheapest class AWS offers.