S3 Object Storage
Store objects durably in S3, control access, and pick the right storage class.
S3 is object storage: you put objects (files + metadata) into buckets with globally unique names. It’s famously durable — eleven nines (99.999999999%) — and scales infinitely. Objects are accessed by key over HTTPS.
Storage classes trade access cost for storage cost:
- Standard — frequent access
- Intelligent-Tiering — auto-moves objects by access pattern
- Standard-IA / One Zone-IA — infrequent access
- Glacier / Glacier Deep Archive — cheap archival, slower retrieval
Secure with block public access (on by default), bucket policies, IAM, and encryption (SSE-S3/KMS). Lifecycle rules transition or expire objects; versioning protects against overwrites and deletes.
aws s3 mb s3://my-unique-bucket-name
aws s3 cp report.pdf s3://my-unique-bucket-name/reports/
aws s3 ls s3://my-unique-bucket-name/reports/
# Presigned URL: temporary access without making the object public
aws s3 presign s3://my-unique-bucket-name/reports/report.pdf --expires-in 3600- Choose a storage class for: a live website’s images, monthly backups, 7-year archives.
- Explain how a presigned URL shares an object without making the bucket public.
- Describe a lifecycle rule that moves objects to Glacier after 90 days.
- Why does S3 require globally unique bucket names?
Cheat Sheet▾
| Feature | Detail |
|---|---|
| Durability | 11 nines (99.999999999%) |
| Standard | Frequent access |
| Intelligent-Tiering | Auto-tiers by access |
| Glacier | Cheap archival, slow retrieval |
| Block Public Access | On by default — keep it |
| Versioning | Protects against overwrite/delete |
| Presigned URL | Temporary, scoped access |
Common Interview Questions▾
How durable is S3 and what does that mean?
99.999999999% (eleven nines) durability — S3 redundantly stores objects across multiple devices and facilities, making data loss extraordinarily unlikely.
How do you give someone temporary access to a private S3 object?
Generate a presigned URL with an expiry, which grants time-limited access to that specific object without changing bucket permissions or making it public.
What are S3 storage classes for?
To match cost to access pattern — Standard for hot data, Standard-IA for infrequent, and Glacier classes for cheap long-term archival with slower retrieval.