Emitting API Events

Overview

Build event-driven API architectures using outbound webhooks, Server-Sent Events (SSE), and message broker integration. Implement event emission from API mutations, event schema registry, subscriber management, delivery guarantees with retry logic, and event sourcing patterns for maintaining a complete audit log of API state changes.

Prerequisites

• Message broker: Redis Pub/Sub, RabbitMQ, Apache Kafka, or AWS SNS/SQS
• Persistent storage for event log and subscriber registrations (PostgreSQL, MongoDB)
• Webhook delivery infrastructure with retry queue (Bull, Celery, or managed service)
• Event schema registry for versioned event type definitions
• SSE-capable web framework for real-time event streaming to browser clients

Instructions

1. Identify event-producing operations using Grep and Read, cataloging every API mutation (POST, PUT, PATCH, DELETE) that should emit events, with event type names following resource.action convention (e.g., order.created, user.updated).
2. Define event schemas for each event type with versioning: include eventId (UUID), eventType, version, timestamp (ISO 8601), source (service identifier), and data (type-specific payload).
3. Implement the event emitter service that publishes events to the message broker after successful API mutations, using the transactional outbox pattern to ensure events are not lost on application crash.
4. Build a webhook subscription management API: POST /webhooks (subscribe), GET /webhooks (list), DELETE /webhooks/:id (unsubscribe), with URL validation, event type filtering, and signing secret generation.
5. Implement webhook delivery with HMAC-SHA256 signed payloads, configurable retry policy (exponential backoff: 1min, 5min, 30min, 2hr, 24hr), and automatic subscription deactivation after consecutive failures.
6. Add Server-Sent Events endpoint (GET /events/stream) for real-time event delivery to browser clients, with Last-Event-ID support for reconnection and missed event replay.
7. Create a dead-letter queue for events that exhaust all delivery retry attempts, with alerting and manual replay capability.
8. Write integration tests covering event emission, webhook delivery with signature verification, SSE stream connection with reconnection, and dead-letter queue behavior.

See ${CLAUDESKILLDIR}/references/implementation.md for the full implementation guide.

Output

• ${CLAUDESKILLDIR}/src/events/emitter.js - Event emission service with outbox pattern
• ${CLAUDESKILLDIR}/src/events/schemas/ - Versioned event type schema definitions