System Design: Multi‑Tenant Cloud Storage Service (Take‑Home)

You are tasked with designing a multi‑tenant cloud storage service that supports file upload, retrieval, copy, compression, quotas, and strong operational guarantees. Assume a typical public cloud environment and that tenants may have multiple buckets or namespaces.

Requirements

1. APIs and Copy Semantics
   • Define REST APIs for: uploading new files, retrieving files, copying files, deleting files, and listing.
   • Define copy semantics for: server‑side copy, deep copy, and copy‑on‑write (CoW).
   • Specify how metadata (e.g., content‑type, custom key/values) and permissions propagate during copy.
2. Multi‑Tenant Users and Quotas
   • Support adding users/tenants with per‑user capacity limits and tiers.
   • Describe quota accounting, enforcement at upload time (including multipart), and how copies and compression count toward quotas.
3. Compression
   • Support compressing on upload and decompressing on download.
   • Choose algorithms and where compression sits in the data path.
   • Specify how compression metadata is stored.
   • Discuss trade‑offs between CPU cost, latency, and storage savings.
4. Durability, Availability, Scalability, Consistency
   • Detail core components (object store, metadata service, index/catalog).
   • Describe partitioning/sharding, replication/erasure coding, background tasks (GC, scrubbing, rebalancing), and failure recovery.
5. Security, Auditing, Versioning, Monitoring
   • Cover authentication and authorization/ACLs and propose APIs/methods.
   • Include auditing, object versioning, and monitoring/alerting.
   • Outline tests to validate these features.