event

Event -- Event-Driven Architecture

Activate When

• User invokes /godmode:event
• User says "event sourcing", "CQRS", "message broker"
• User says "Kafka", "RabbitMQ", "dead letter queue"
• When building loosely coupled async systems

Workflow

Step 1: Event Architecture Assessment

# Detect message broker infrastructure
ls kafka/ docker-compose*.yml 2>/dev/null \
  | head -5
grep -rl "kafkajs\|amqplib\|@aws-sdk/client-sqs" \
  package.json pyproject.toml 2>/dev/null

# Check for event schemas
find . -name "*.avsc" -o -name "*.proto" \
  -o -path "*/events/*" | head -10

EVENT ARCHITECTURE CONTEXT:
Current State: No events | Basic pub/sub | Full CQRS/ES
Throughput: <events per second>
Ordering: None | Per-entity | Global
Retention: <how long to store events>

IF throughput > 10K/s: recommend Kafka
IF ordering per-entity only: Kafka partitions by key
IF need replay: Kafka or NATS JetStream (not RabbitMQ)
IF simple fan-out: SNS/SQS or RabbitMQ

Step 2: Broker Selection

MESSAGE BROKER SELECTION:
| Feature    | Kafka  | RabbitMQ | SQS/SNS | NATS  |
|-----------|--------|----------|---------|-------|
| Throughput| V.High | High     | High    | V.High|
| Latency   | ~5ms   | ~1ms     | ~50ms   | ~0.1ms|
| Ordering  | Per-pt | Per-q    | FIFO opt| Per-sb|
| Replay    | Yes    | No       | No      | Yes*  |

THRESHOLDS:
  Kafka: use when > 10K events/sec or need replay
  RabbitMQ: use when < 10K/sec and need routing
  SQS/SNS: use when AWS-native and < 50K/sec
  NATS: use when need sub-ms latency

Step 3: Event Schema Design

EVENT ENVELOPE (required fields):
  event_id: UUID
  event_type: "order.placed" (past tense)
  event_version: "1.2"
  source: "order-service"
  timestamp: ISO 8601
  correlation_id: UUID (propagated across services)
  data: { ... payload ... }

VERSIONING:
  Backward compatible: new schema reads old data
  Forward compatible: old schema reads new data
  RULE: never modify existing fields, only add
  RULE: new fields must have defaults
  RULE: reserve removed field numbers (protobuf)