Distributed Unique ID Generator (Snowflake) — Simple

Problem statement (interviewer prompt)

Design a distributed ID generator that produces globally unique, roughly time-sortable 64-bit IDs at 10k+ IDs/sec/node across hundreds of nodes — without a central coordinator on the hot path and without duplicates after process restarts.

flowchart LR
  C([Client / Service])
  S[ID Server]
  T[Wall clock ms]
  M[Machine ID]
  N[Sequence per ms]
  C --> S
  T --> S
  M --> S
  N --> S
  S -->|64-bit ID| C

    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 S,T,M,N service;

ID = [1 sign | 41 ms timestamp | 10 machine | 12 sequence] = 64 bits, sortable, decentralized.