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┌─────────────┐ ┌─────────────┐ ┌─────────────┐
│ Service A │ │ Service B │ │ Service C │
│ ┌─────────┐ │ │ ┌─────────┐ │ │ ┌─────────┐ │
│ │ DB A │ │ │ │ DB B │ │ │ │ DB C │ │
│ └─────────┘ │ │ └─────────┘ │ │ └─────────┘ │
└─────┬───────┘ └─────┬───────┘ └─────┬───────┘
│ API/Event │ API/Event │ API/Event
└─────────────────────┴─────────────────────┴This diagram shows three microservices, each with its own private database. They communicate only via APIs or events, never sharing databases directly.
### Before: Two services sharing the same database table directly class OrderService: def create_order(self, order_data): # Directly insert into shared orders table db.execute("INSERT INTO orders ...", order_data) class PaymentService: def update_payment_status(self, order_id, status): # Directly update shared orders table db.execute("UPDATE orders SET payment_status=? WHERE id=?", (status, order_id)) ### After: Each service owns its own database and communicates via API # Order Service with private DB class OrderService: def __init__(self, db, event_bus): self.db = db self.event_bus = event_bus def create_order(self, order_data): self.db.insert_order(order_data) # Notify Payment Service via event self.event_bus.publish('order_created', order_data) # Payment Service with private DB class PaymentService: def __init__(self, db): self.db = db def on_order_created(self, order_data): self.db.create_payment_record(order_data['id']) def update_payment_status(self, order_id, status): self.db.update_payment_status(order_id, status) # Event bus simulates communication class EventBus: def __init__(self): self.subscribers = {} def publish(self, event, data): for handler in self.subscribers.get(event, []): handler(data) def subscribe(self, event, handler): self.subscribers.setdefault(event, []).append(handler) # Wiring up # Assuming db instances are provided order_db = ... # some database instance for orders payment_db = ... # some database instance for payments event_bus = EventBus() order_service = OrderService(order_db, event_bus) payment_service = PaymentService(payment_db) event_bus.subscribe('order_created', payment_service.on_order_created) # Explanation: # The OrderService owns its orders database and publishes events. # The PaymentService owns its payment database and reacts to events. # No direct database sharing occurs.