What is Microservices?

Definition

Microservices architecture decomposes an application into small, autonomous services that can be developed, deployed, and scaled independently. Each service owns its data and business logic, communicating with other services through well-defined APIs or asynchronous messaging.

This contrasts with monolithic architecture, where all functionality lives in a single, tightly-coupled codebase. Microservices gained mainstream adoption through companies like Netflix, Amazon, and Uber.

Core Principles

• Single responsibility: Each service handles one business capability (users, payments, notifications).
• Independent deployment: Services can be deployed without affecting others.
• Decentralized data: Each service manages its own database - no shared databases.
• Fault isolation: Failure in one service doesn't cascade to the entire system.
• Technology agnostic: Each service can use different languages, frameworks, and databases.
• API-first communication: Services communicate through REST APIs, gRPC, or message queues.

When to Use Microservices

Microservices aren't always the answer. Consider them when:

• Your team is large enough to own separate services (typically 50+ engineers)
• Different parts of your system need to scale independently
• You need independent deployment cycles for different features
• Your domain has clear bounded contexts

Start with a monolith if you're a startup or small team. It's easier to extract microservices from a well-structured monolith than to merge poorly-designed microservices. Many successful companies started monolithic and transitioned as they grew.

Code Example

# Service A: User Service (FastAPI)
@app.post("/users/")
async def create_user(user: UserCreate):
    new_user = await db.create_user(user)
    # Publish event for other services
    await message_broker.publish("user.created", new_user.dict())
    return new_user

# Service B: Notification Service (separate process)
@broker.subscriber("user.created")
async def handle_user_created(event: dict):
    await send_welcome_email(event["email"])
    await create_default_preferences(event["id"])

Frequently Asked Questions

When should I use microservices vs monolith?

Start with a monolith for new projects and small teams. Microservices add significant operational complexity (distributed tracing, service discovery, eventual consistency). Move to microservices when your team grows, deployment bottlenecks appear, or different components need independent scaling.

What are the biggest challenges with microservices?

Distributed systems complexity is the biggest challenge. This includes: data consistency across services, distributed transactions, service discovery, network failures, debugging across service boundaries, and operational overhead of managing many deployments. You need mature DevOps practices.