Walk me through the main S3 storage classes and how you would use lifecycle policies to control cost.
What they are really testing: Whether you can match access patterns to storage classes and know the retrieval/minimum-duration gotchas, not just "Glacier is cheap".
A real interview question
Walk me through the main S3 storage classes and how you would use lifecycle policies to control cost.
What most people say
drag me
“There is S3 Standard for normal storage and Glacier for cheap long-term storage, and you can move data to Glacier to save money.”
It collapses many classes into two and ignores the practical traps: IA retrieval fees, minimum storage durations, and Glacier restore times. Moving frequently-read data to Glacier can cost more, not less.
The follow-ups they ask next
When would moving data to Glacier actually cost more?
If you still read it often: Glacier has retrieval fees and minimum storage durations, plus restore latency. Frequently accessed data belongs in Standard or IA, not archive tiers.
When is Intelligent-Tiering the right default?
When access patterns are unpredictable or unknown. It auto-tiers for a small per-object monitoring fee, avoiding both manual lifecycle guesswork and accidental retrieval-fee surprises.
What the interviewer is listening for
- Matches class to access pattern
- Knows IA retrieval fee + 30-day minimum
- Automates with lifecycle policies
What sinks the answer
- Only Standard and Glacier
- Unaware of retrieval fees / restore times
- Would archive frequently-read data
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“Match class to access: [Standard for hot, Standard-IA for rare-but-instant with a retrieval fee + 30-day min, Intelligent-Tiering when access is unknown, Glacier tiers for archive, cheaper as retrieval gets slower]. Automate with [lifecycle policies: Standard to IA to Glacier to expire]. Watch [minimum durations and retrieval fees, archiving hot data can cost more].”
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