Microservices Architecture

Monolith vs Microservices

Monolith:

One big application
├── User management
├── Orders
├── Payments
└── Notifications

All in one codebase, one database, one deployment

Microservices:

Multiple small services
├── User Service (port 3001)
├── Order Service (port 3002)
├── Payment Service (port 3003)
└── Notification Service (port 3004)

Each has own codebase, database, deployment

Benefits

• Independent deployment - Update one service without affecting others
• Technology flexibility - Use different tech for different services
• Better scalability - Scale only services that need it
• Fault isolation - One service crash doesn't kill everything

Basic Service Structure

// user-service/index.js
const express = require('express');
const app = express();

app.get('/users/:id', async (req, res) => {
  const user = await User.findById(req.params.id);
  res.json(user);
});

app.listen(3001);

// order-service/index.js
const express = require('express');
const app = express();

app.get('/orders/:id', async (req, res) => {
  const order = await Order.findById(req.params.id);
  res.json(order);
});

app.listen(3002);

Service Communication

const axios = require('axios');

app.get('/orders/:id', async (req, res) => {
  const order = await Order.findById(req.params.id);
  
  const userResponse = await axios.get(
    `http://user-service:3001/users/${order.userId}`
  );
  
  res.json({
    ...order.toObject(),
    user: userResponse.data
  });
});

API Gateway

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');

const app = express();

app.use('/api/users', createProxyMiddleware({
  target: 'http://user-service:3001',
  changeOrigin: true
}));

app.use('/api/orders', createProxyMiddleware({
  target: 'http://order-service:3002',
  changeOrigin: true
}));

app.listen(3000);

Key Takeaway

Microservices enable independent scaling and deployment. Use API gateway as entry point. Each service has own database. Start simple, split when needed.