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

Order Service

class OrderService: async def create_order(self, order_data: dict) -> Order: order = Order.create(order_data) await self.event_bus.publish( OrderCreatedEvent(order_id=order.id, customer_id=order.customer_id) ) return order

Payment Service (separate service)

class PaymentService: async def process_payment(self, payment_request: PaymentRequest) -> PaymentResult: 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) ) return result

Inventory Service (separate service)

class InventoryService: async def reserve_items(self, order_id: str, items: List[OrderItem]) -> ReservationResult: 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")

    reservation = await self.create_reservation(order_id, items)
    await self.event_bus.publish(InventoryReservedEvent(order_id=order_id))
    return ReservationResult(success=True, reservation=reservation)

Pattern 2: API Gateway

from fastapi import FastAPI import httpx

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.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."""
    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
    )

    result = {"order": order}
    if not isinstance(payment, Exception):
        result["payment"] = payment
    if not isinstance(inventory, Exception):
        result["inventory"] = inventory
    return result

Communication Patterns

Pattern 1: Synchronous REST Communication

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))

@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()

payment_client = ServiceClient("http://payment-service:8001") result = await payment_client.get("/payments/123")

Pattern 2: Asynchronous Event-Driven

from aiokafka import AIOKafkaProducer, AIOKafkaConsumer import json

class EventBus: """Event publishing and subscription."""

async def publish(self, event: DomainEvent):
    """Publish event to Kafka topic."""
    await self.producer.send_and_wait(
        event.event_type,
        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)
    await consumer.start()
    async for message in consumer:
        await handler(message.value)

Order Service publishes

await event_bus.publish(OrderCreatedEvent(order_id=order.id))

Inventory Service subscribes

async def handle_order_created(event_data: dict): await reserve_inventory(event_data["order_id"], event_data["items"])

Pattern 3: Saga Pattern (Distributed Transactions)

class OrderFulfillmentSaga: """Orchestrated saga for order fulfillment."""

def __init__(self):
    self.steps = [
        SagaStep("create_order", self.create_order, self.cancel_order),
        SagaStep("reserve_inventory", self.reserve_inventory, self.release_inventory),
        SagaStep("process_payment", self.process_payment, self.refund_payment),
        SagaStep("confirm_order", self.confirm_order, self.cancel_order_confirmation)
    ]

async def execute(self, order_data: dict) -> SagaResult:
    completed_steps = []
    context = {"order_data": order_data}

    try:
        for step in self.steps:
            result = await step.action(context)
            if not result.success:
                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:
        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):
        await step.compensation(context)

Resilience Patterns

Circuit Breaker Pattern

from enum import Enum from datetime import datetime, timedelta

class CircuitState(Enum): CLOSED = "closed" # Normal operation OPEN = "open" # Failing, reject requests HALF_OPEN = "half_open" # Testing recovery

class CircuitBreaker: def init(self, failure_threshold: int = 5, recovery_timeout: int = 30): self.failure_threshold = failure_threshold self.recovery_timeout = recovery_timeout self.failure_count = 0 self.state = CircuitState.CLOSED self.opened_at = None

async def call(self, func, *args, **kwargs):
    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):
    self.failure_count = 0
    if self.state == CircuitState.HALF_OPEN:
        self.state = CircuitState.CLOSED

def _on_failure(self):
    self.failure_count += 1
    if self.failure_count >= self.failure_threshold:
        self.state = CircuitState.OPEN
        self.opened_at = datetime.now()

breaker = CircuitBreaker(failure_threshold=5, recovery_timeout=30) result = await breaker.call(payment_client.process_payment, payment_data)

Best Practices

• Service Boundaries: Align with business capabilities

• Database Per Service: No shared databases

• API Contracts: Versioned, backward compatible

• Async When Possible: Events over direct calls

• Circuit Breakers: Fail fast on service failures

• Distributed Tracing: Track requests across services

• Service Registry: Dynamic service discovery

• 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