Background Job Processing — Simple

Problem statement (interviewer prompt)

Design a background-job processing system (Celery / Sidekiq scale). Producers enqueue jobs, workers process them with retries + backoff + DLQ, support delayed jobs, periodic jobs, prioritisation, and 100k+ jobs/s with at-least-once delivery + idempotent handlers.

flowchart LR
  APP[App]
  Q[[(Job queue)]]
  W([Workers])
  RES[(Result store)]
  APP --> Q --> W --> RES

    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 APP service;
    class Q,RES datastore;
    class W compute;