Distributed Cache — Simple

Problem statement (interviewer prompt)

Design a distributed in-memory cache (Redis/Memcached cluster). Support sub-millisecond GET/SET at 1M+ ops/s, sharding, replication, eviction (LRU/LFU/TTL), and handle the operational pitfalls — cache stampedes, hot keys, big keys, mass-expiry storms.

flowchart LR
  C[App]
  R([Client<br/>consistent hash])
  N1[(Cache 1)]
  N2[(Cache 2)]
  N3[(Cache 3)]
  C --> R
  R --> N1
  R --> N2
  R --> N3

    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 R client;
    class C service;
    class N1,N2,N3 datastore;