What are the S3 storage classes and when do you use each?
Quick Answer
Standard (frequent access), Standard-IA and One Zone-IA (infrequent access, lower storage cost, retrieval fee), Glacier Instant/Flexible and Glacier Deep Archive (archival, cheapest, higher retrieval latency), and Intelligent-Tiering (auto-moves objects between tiers by access pattern).
Detailed Answer
The trade-off is storage price vs access cost/latency and durability/AZ scope. One Zone-IA is cheaper but stores in a single AZ (less resilient). Use lifecycle policies to transition objects automatically (e.g., Standard to IA after 30 days to Glacier after 90), and Intelligent-Tiering when access patterns are unpredictable so you do not have to tune it.
Interview Tip
Explain the price-vs-access/latency trade-off and mention lifecycle policies to transition objects automatically — that is how the classes are used in practice.