Microservices Design

Service Boundaries

Define services around business capabilities, not technical layers. Each service owns its data store and exposes a clear API contract.

order-service/       -> owns orders table, publishes OrderCreated events
inventory-service/   -> owns inventory table, subscribes to OrderCreated
payment-service/     -> owns payments table, handles payment processing
notification-service -> stateless, subscribes to events, sends emails/SMS

Event-Driven Communication

interface DomainEvent {
  eventId: string;
  eventType: string;
  aggregateId: string;
  timestamp: string;
  version: number;
  payload: Record<string, unknown>;
}

const orderCreatedEvent: DomainEvent = {
  eventId: crypto.randomUUID(),
  eventType: "order.created",
  aggregateId: orderId,
  timestamp: new Date().toISOString(),
  version: 1,
  payload: { customerId, items, totalAmount },
};

await broker.publish("orders", orderCreatedEvent);

async function handleOrderCreated(event: DomainEvent) {
  const { items } = event.payload as OrderPayload;

  for (const item of items) {
    await db.inventory.update({
      where: { productId: item.productId },
      data: { quantity: { decrement: item.quantity } },
    });
  }

  await markEventProcessed(event.eventId);
}

Use idempotency keys (eventId) to handle duplicate deliveries safely.

Saga Pattern (Orchestration)