Pattern 16 / COMMS

Webhooks

Use this when notifying an external system exactly when something happens.

Pressure
Notifying an external system exactly when something happens
Mechanism
Store a subscriber url and post event payloads to it with retries and signatures
Toll
The receiver must be reachable, verify signatures, retry safely, and handle duplicates
Architecture plate16
Diagram for Webhooks
Executive brief

Webhooks fits when notifying an external system exactly when something happens. Mechanism: store a subscriber URL and POST event payloads to it with retries and signatures. Use it for third-party integrations, SaaS callbacks, payment processors, and Git events. The toll: the receiver must be reachable, verify signatures, retry safely, and handle duplicates.

Use when

Third-party integrations, saas callbacks, payment processors, and git events.

Example

Payment provider sending invoice.paid to a merchant endpoint.

Review framing

Describe the pressure first, then the mechanism, then the cost. That keeps the design grounded.

Same pressure family

Communication Patterns

12Request-Response (Synchronous)13Message Queue (Asynchronous)14Publish-Subscribe (Pub/Sub)15Event-Driven Architecture17Server-Sent Events (SSE)18Bidirectional Streaming (WebSockets / gRPC Streaming)
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