Webhooks System — Simple

Problem statement (interviewer prompt)

Design a webhooks delivery service: publishers register subscribers, when an event fires you POST to every subscriber URL with idempotent retries, exponential backoff, signing for authenticity, a dead-letter queue for failures, and a manual-replay UI.

flowchart LR
  PROD[Producer Service]
  Q[[(Outbound queue)]]
  DEL([Delivery Workers])
  CUS([Customer Endpoint])
  DLQ[[(DLQ)]]
  PROD --> Q --> DEL --> CUS
  DEL --> DLQ

    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 CUS client;
    class PROD service;
    class Q,DLQ datastore;
    class DEL compute;