Webhook System

Five concerns that must each be correct independently: subscription management, delivery, signing, failure tracking, and re-delivery. A mistake in any one breaks the whole contract with consumers.

Phase 1: Discovery

Before writing any code:

What triggers webhooks?

• Domain events from DB writes (user.created, payment.succeeded) — or any state change?
• Who emits events: one service or multiple? If multiple, a shared event bus is needed; per-service pub/sub is not enough
• Are events ordered? Consumers often assume ordering per-entity; delivery order is not guaranteed across retries unless explicitly designed for

What's the delivery guarantee requirement?

• At-least-once (standard, acceptable duplicates) — use idempotency keys on consumer side
• Exactly-once — not achievable at the transport layer; requires idempotent consumers + deduplication window