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+---
+name: microservices-patterns
+description: Design microservices architectures with service boundaries, event-driven communication, and resilience patterns. Use when building distributed systems, decomposing monoliths, or implementing microservices.
+---
+
+# Microservices Patterns
+
+Master microservices architecture patterns including service boundaries, inter-service communication, data management, and resilience patterns for building distributed systems.
+
+## When to Use This Skill
+
+- Decomposing monoliths into microservices
+- Designing service boundaries and contracts
+- Implementing inter-service communication
+- Managing distributed data and transactions
+- Building resilient distributed systems
+- Implementing service discovery and load balancing
+- Designing event-driven architectures
+
+## Core Concepts
+
+### 1. Service Decomposition Strategies
+
+**By Business Capability**
+- Organize services around business functions
+- Each service owns its domain
+- Example: OrderService, PaymentService, InventoryService
+
+**By Subdomain (DDD)**
+- Core domain, supporting subdomains
+- Bounded contexts map to services
+- Clear ownership and responsibility
+
+**Strangler Fig Pattern**
+- Gradually extract from monolith
+- New functionality as microservices
+- Proxy routes to old/new systems
+
+### 2. Communication Patterns
+
+**Synchronous (Request/Response)**
+- REST APIs
+- gRPC
+- GraphQL
+
+**Asynchronous (Events/Messages)**
+- Event streaming (Kafka)
+- Message queues (RabbitMQ, SQS)
+- Pub/Sub patterns
+
+### 3. Data Management
+
+**Database Per Service**
+- Each service owns its data
+- No shared databases
+- Loose coupling
+
+**Saga Pattern**
+- Distributed transactions
+- Compensating actions
+- Eventual consistency
+
+### 4. Resilience Patterns
+
+**Circuit Breaker**
+- Fail fast on repeated errors
+- Prevent cascade failures
+
+**Retry with Backoff**
+- Transient fault handling
+- Exponential backoff
+
+**Bulkhead**
+- Isolate resources
+- Limit impact of failures
+
+## Service Decomposition Patterns
+
+### Pattern 1: By Business Capability
+
+```python
+# E-commerce example
+
+# Order Service
+class OrderService:
+    """Handles order lifecycle."""
+
+    async def create_order(self, order_data: dict) -> Order:
+        order = Order.create(order_data)
+
+        # Publish event for other services
+        await self.event_bus.publish(
+            OrderCreatedEvent(
+                order_id=order.id,
+                customer_id=order.customer_id,
+                items=order.items,
+                total=order.total
+            )
+        )
+
+        return order
+
+# Payment Service (separate service)
+class PaymentService:
+    """Handles payment processing."""
+
+    async def process_payment(self, payment_request: PaymentRequest) -> PaymentResult:
+        # Process payment
+        result = await self.payment_gateway.charge(
+            amount=payment_request.amount,
+            customer=payment_request.customer_id
+        )
+
+        if result.success:
+            await self.event_bus.publish(
+                PaymentCompletedEvent(
+                    order_id=payment_request.order_id,
+                    transaction_id=result.transaction_id
+                )
+            )
+
+        return result
+
+# Inventory Service (separate service)
+class InventoryService:
+    """Handles inventory management."""
+
+    async def reserve_items(self, order_id: str, items: List[OrderItem]) -> ReservationResult:
+        # Check availability
+        for item in items:
+            available = await self.inventory_repo.get_available(item.product_id)
+            if available < item.quantity:
+                return ReservationResult(
+                    success=False,
+                    error=f"Insufficient inventory for {item.product_id}"
+                )
+
+        # Reserve items
+        reservation = await self.create_reservation(order_id, items)
+
+        await self.event_bus.publish(
+            InventoryReservedEvent(
+                order_id=order_id,
+                reservation_id=reservation.id
+            )
+        )
+
+        return ReservationResult(success=True, reservation=reservation)
+```
+
+### Pattern 2: API Gateway
+
+```python
+from fastapi import FastAPI, HTTPException, Depends
+import httpx
+from circuitbreaker import circuit
+
+app = FastAPI()
+
+class APIGateway:
+    """Central entry point for all client requests."""
+
+    def __init__(self):
+        self.order_service_url = "http://order-service:8000"
+        self.payment_service_url = "http://payment-service:8001"
+        self.inventory_service_url = "http://inventory-service:8002"
+        self.http_client = httpx.AsyncClient(timeout=5.0)
+
+    @circuit(failure_threshold=5, recovery_timeout=30)
+    async def call_order_service(self, path: str, method: str = "GET", **kwargs):
+        """Call order service with circuit breaker."""
+        response = await self.http_client.request(
+            method,
+            f"{self.order_service_url}{path}",
+            **kwargs
+        )
+        response.raise_for_status()
+        return response.json()
+
+    async def create_order_aggregate(self, order_id: str) -> dict:
+        """Aggregate data from multiple services."""
+        # Parallel requests
+        order, payment, inventory = await asyncio.gather(
+            self.call_order_service(f"/orders/{order_id}"),
+            self.call_payment_service(f"/payments/order/{order_id}"),
+            self.call_inventory_service(f"/reservations/order/{order_id}"),
+            return_exceptions=True
+        )
+
+        # Handle partial failures
+        result = {"order": order}
+        if not isinstance(payment, Exception):
+            result["payment"] = payment
+        if not isinstance(inventory, Exception):
+            result["inventory"] = inventory
+
+        return result
+
+@app.post("/api/orders")
+async def create_order(
+    order_data: dict,
+    gateway: APIGateway = Depends()
+):
+    """API Gateway endpoint."""
+    try:
+        # Route to order service
+        order = await gateway.call_order_service(
+            "/orders",
+            method="POST",
+            json=order_data
+        )
+        return {"order": order}
+    except httpx.HTTPError as e:
+        raise HTTPException(status_code=503, detail="Order service unavailable")
+```
+
+## Communication Patterns
+
+### Pattern 1: Synchronous REST Communication
+
+```python
+# Service A calls Service B
+import httpx
+from tenacity import retry, stop_after_attempt, wait_exponential
+
+class ServiceClient:
+    """HTTP client with retries and timeout."""
+
+    def __init__(self, base_url: str):
+        self.base_url = base_url
+        self.client = httpx.AsyncClient(
+            timeout=httpx.Timeout(5.0, connect=2.0),
+            limits=httpx.Limits(max_keepalive_connections=20)
+        )
+
+    @retry(
+        stop=stop_after_attempt(3),
+        wait=wait_exponential(multiplier=1, min=2, max=10)
+    )
+    async def get(self, path: str, **kwargs):
+        """GET with automatic retries."""
+        response = await self.client.get(f"{self.base_url}{path}", **kwargs)
+        response.raise_for_status()
+        return response.json()
+
+    async def post(self, path: str, **kwargs):
+        """POST request."""
+        response = await self.client.post(f"{self.base_url}{path}", **kwargs)
+        response.raise_for_status()
+        return response.json()
+
+# Usage
+payment_client = ServiceClient("http://payment-service:8001")
+result = await payment_client.post("/payments", json=payment_data)
+```
+
+### Pattern 2: Asynchronous Event-Driven
+
+```python
+# Event-driven communication with Kafka
+from aiokafka import AIOKafkaProducer, AIOKafkaConsumer
+import json
+from dataclasses import dataclass, asdict
+from datetime import datetime
+
+@dataclass
+class DomainEvent:
+    event_id: str
+    event_type: str
+    aggregate_id: str
+    occurred_at: datetime
+    data: dict
+
+class EventBus:
+    """Event publishing and subscription."""
+
+    def __init__(self, bootstrap_servers: List[str]):
+        self.bootstrap_servers = bootstrap_servers
+        self.producer = None
+
+    async def start(self):
+        self.producer = AIOKafkaProducer(
+            bootstrap_servers=self.bootstrap_servers,
+            value_serializer=lambda v: json.dumps(v).encode()
+        )
+        await self.producer.start()
+
+    async def publish(self, event: DomainEvent):
+        """Publish event to Kafka topic."""
+        topic = event.event_type
+        await self.producer.send_and_wait(
+            topic,
+            value=asdict(event),
+            key=event.aggregate_id.encode()
+        )
+
+    async def subscribe(self, topic: str, handler: callable):
+        """Subscribe to events."""
+        consumer = AIOKafkaConsumer(
+            topic,
+            bootstrap_servers=self.bootstrap_servers,
+            value_deserializer=lambda v: json.loads(v.decode()),
+            group_id="my-service"
+        )
+        await consumer.start()
+
+        try:
+            async for message in consumer:
+                event_data = message.value
+                await handler(event_data)
+        finally:
+            await consumer.stop()
+
+# Order Service publishes event
+async def create_order(order_data: dict):
+    order = await save_order(order_data)
+
+    event = DomainEvent(
+        event_id=str(uuid.uuid4()),
+        event_type="OrderCreated",
+        aggregate_id=order.id,
+        occurred_at=datetime.now(),
+        data={
+            "order_id": order.id,
+            "customer_id": order.customer_id,
+            "total": order.total
+        }
+    )
+
+    await event_bus.publish(event)
+
+# Inventory Service listens for OrderCreated
+async def handle_order_created(event_data: dict):
+    """React to order creation."""
+    order_id = event_data["data"]["order_id"]
+    items = event_data["data"]["items"]
+
+    # Reserve inventory
+    await reserve_inventory(order_id, items)
+```
+
+### Pattern 3: Saga Pattern (Distributed Transactions)
+
+```python
+# Saga orchestration for order fulfillment
+from enum import Enum
+from typing import List, Callable
+
+class SagaStep:
+    """Single step in saga."""
+
+    def __init__(
+        self,
+        name: str,
+        action: Callable,
+        compensation: Callable
+    ):
+        self.name = name
+        self.action = action
+        self.compensation = compensation
+
+class SagaStatus(Enum):
+    PENDING = "pending"
+    COMPLETED = "completed"
+    COMPENSATING = "compensating"
+    FAILED = "failed"
+
+class OrderFulfillmentSaga:
+    """Orchestrated saga for order fulfillment."""
+
+    def __init__(self):
+        self.steps: List[SagaStep] = [
+            SagaStep(
+                "create_order",
+                action=self.create_order,
+                compensation=self.cancel_order
+            ),
+            SagaStep(
+                "reserve_inventory",
+                action=self.reserve_inventory,
+                compensation=self.release_inventory
+            ),
+            SagaStep(
+                "process_payment",
+                action=self.process_payment,
+                compensation=self.refund_payment
+            ),
+            SagaStep(
+                "confirm_order",
+                action=self.confirm_order,
+                compensation=self.cancel_order_confirmation
+            )
+        ]
+
+    async def execute(self, order_data: dict) -> SagaResult:
+        """Execute saga steps."""
+        completed_steps = []
+        context = {"order_data": order_data}
+
+        try:
+            for step in self.steps:
+                # Execute step
+                result = await step.action(context)
+                if not result.success:
+                    # Compensate
+                    await self.compensate(completed_steps, context)
+                    return SagaResult(
+                        status=SagaStatus.FAILED,
+                        error=result.error
+                    )
+
+                completed_steps.append(step)
+                context.update(result.data)
+
+            return SagaResult(status=SagaStatus.COMPLETED, data=context)
+
+        except Exception as e:
+            # Compensate on error
+            await self.compensate(completed_steps, context)
+            return SagaResult(status=SagaStatus.FAILED, error=str(e))
+
+    async def compensate(self, completed_steps: List[SagaStep], context: dict):
+        """Execute compensating actions in reverse order."""
+        for step in reversed(completed_steps):
+            try:
+                await step.compensation(context)
+            except Exception as e:
+                # Log compensation failure
+                print(f"Compensation failed for {step.name}: {e}")
+
+    # Step implementations
+    async def create_order(self, context: dict) -> StepResult:
+        order = await order_service.create(context["order_data"])
+        return StepResult(success=True, data={"order_id": order.id})
+
+    async def cancel_order(self, context: dict):
+        await order_service.cancel(context["order_id"])
+
+    async def reserve_inventory(self, context: dict) -> StepResult:
+        result = await inventory_service.reserve(
+            context["order_id"],
+            context["order_data"]["items"]
+        )
+        return StepResult(
+            success=result.success,
+            data={"reservation_id": result.reservation_id}
+        )
+
+    async def release_inventory(self, context: dict):
+        await inventory_service.release(context["reservation_id"])
+
+    async def process_payment(self, context: dict) -> StepResult:
+        result = await payment_service.charge(
+            context["order_id"],
+            context["order_data"]["total"]
+        )
+        return StepResult(
+            success=result.success,
+            data={"transaction_id": result.transaction_id},
+            error=result.error
+        )
+
+    async def refund_payment(self, context: dict):
+        await payment_service.refund(context["transaction_id"])
+```
+
+## Resilience Patterns
+
+### Circuit Breaker Pattern
+
+```python
+from enum import Enum
+from datetime import datetime, timedelta
+from typing import Callable, Any
+
+class CircuitState(Enum):
+    CLOSED = "closed"  # Normal operation
+    OPEN = "open"      # Failing, reject requests
+    HALF_OPEN = "half_open"  # Testing if recovered
+
+class CircuitBreaker:
+    """Circuit breaker for service calls."""
+
+    def __init__(
+        self,
+        failure_threshold: int = 5,
+        recovery_timeout: int = 30,
+        success_threshold: int = 2
+    ):
+        self.failure_threshold = failure_threshold
+        self.recovery_timeout = recovery_timeout
+        self.success_threshold = success_threshold
+
+        self.failure_count = 0
+        self.success_count = 0
+        self.state = CircuitState.CLOSED
+        self.opened_at = None
+
+    async def call(self, func: Callable, *args, **kwargs) -> Any:
+        """Execute function with circuit breaker."""
+
+        if self.state == CircuitState.OPEN:
+            if self._should_attempt_reset():
+                self.state = CircuitState.HALF_OPEN
+            else:
+                raise CircuitBreakerOpenError("Circuit breaker is open")
+
+        try:
+            result = await func(*args, **kwargs)
+            self._on_success()
+            return result
+
+        except Exception as e:
+            self._on_failure()
+            raise
+
+    def _on_success(self):
+        """Handle successful call."""
+        self.failure_count = 0
+
+        if self.state == CircuitState.HALF_OPEN:
+            self.success_count += 1
+            if self.success_count >= self.success_threshold:
+                self.state = CircuitState.CLOSED
+                self.success_count = 0
+
+    def _on_failure(self):
+        """Handle failed call."""
+        self.failure_count += 1
+
+        if self.failure_count >= self.failure_threshold:
+            self.state = CircuitState.OPEN
+            self.opened_at = datetime.now()
+
+        if self.state == CircuitState.HALF_OPEN:
+            self.state = CircuitState.OPEN
+            self.opened_at = datetime.now()
+
+    def _should_attempt_reset(self) -> bool:
+        """Check if enough time passed to try again."""
+        return (
+            datetime.now() - self.opened_at
+            > timedelta(seconds=self.recovery_timeout)
+        )
+
+# Usage
+breaker = CircuitBreaker(failure_threshold=5, recovery_timeout=30)
+
+async def call_payment_service(payment_data: dict):
+    return await breaker.call(
+        payment_client.process_payment,
+        payment_data
+    )
+```
+
+## Resources
+
+- **references/service-decomposition-guide.md**: Breaking down monoliths
+- **references/communication-patterns.md**: Sync vs async patterns
+- **references/saga-implementation.md**: Distributed transactions
+- **assets/circuit-breaker.py**: Production circuit breaker
+- **assets/event-bus-template.py**: Kafka event bus implementation
+- **assets/api-gateway-template.py**: Complete API gateway
+
+## Best Practices
+
+1. **Service Boundaries**: Align with business capabilities
+2. **Database Per Service**: No shared databases
+3. **API Contracts**: Versioned, backward compatible
+4. **Async When Possible**: Events over direct calls
+5. **Circuit Breakers**: Fail fast on service failures
+6. **Distributed Tracing**: Track requests across services
+7. **Service Registry**: Dynamic service discovery
+8. **Health Checks**: Liveness and readiness probes
+
+## Common Pitfalls
+
+- **Distributed Monolith**: Tightly coupled services
+- **Chatty Services**: Too many inter-service calls
+- **Shared Databases**: Tight coupling through data
+- **No Circuit Breakers**: Cascade failures
+- **Synchronous Everything**: Tight coupling, poor resilience
+- **Premature Microservices**: Starting with microservices
+- **Ignoring Network Failures**: Assuming reliable network
+- **No Compensation Logic**: Can't undo failed transactions