Object Storage (S3-like) — Simple

Problem statement (interviewer prompt)

Design an S3-compatible object storage system: durable, eventually unlimited capacity, with PUT/GET/DELETE/LIST by key, multipart upload, versioning, lifecycle transitions to colder tiers, server-side encryption, and 11×9s durability via erasure coding.

flowchart LR
  C([Client])
  GW[REST API Gateway]
  META[(Metadata index<br/>key -> blob loc)]
  BLOB[(Blob nodes<br/>erasure coded)]
  C -->|PUT/GET key| GW
  GW --> META
  GW --> BLOB

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class C client;
    class GW edge;
    class META,BLOB storage;