Building Scalable Microservices with Node.js and Docker

• Handles many requests at the same time

• Uses less memory and works very fast

• Uses JavaScript (easy language, full-stack)

• Works great for APIs (REST, GraphQL)

• Has thousands of ready-made packages (NPM)

• Same environment in development, testing, and production

• Every microservice runs separately

• Perfect fit for scaling up or scaling down services

• Deploy anywhere - Cloud, On-premise, VMs

• Has its own database

• Can restart independently

• Can live on different servers

// user-service/index.js
import express from "express";

const app = express();
app.use(express.json());

app.get("/users", (req, res) => {
  res.json([{ id: 1, name: "Ana" }, { id: 2, name: "John" }]);
});

app.post("/users", (req, res) => {
  const { name } = req.body;
  res.json({ id: Date.now(), name });
});

app.listen(4000, () => {
  console.log("User service running on port 4000");
});

Run normally:

node index.js

Step 2: Dockerize the Service

Create a Dockerfile:

FROM node:18-alpine

WORKDIR /app

COPY package*.json ./
RUN npm install

COPY . .

EXPOSE 4000

CMD ["node", "index.js"]

Build & Start:

docker build -t user-service .
docker run -p 4000:4000 user-service

Your service is now running inside Docker!

Step 3: Run Multiple Services with Docker Compose

docker-compose.yml

version: "3.8"
services:
  user-service:
    build: ./user-service
    ports:
      - "4000:4000"
    depends_on:
      - mongo

  product-service:
    build: ./product-service
    ports:
      - "5000:5000"
    depends_on:
      - mongo

  mongo:
    image: mongo:6
    container_name: mongo-db
    ports:
      - "27017:27017"

Start all together:

docker-compose up --build

Step 4: Service Communication

Two ways:

Example: publish an event after a new user sign-up

import amqp from "amqplib";

async function publishUserEvent(user) {
  const conn = await amqp.connect("amqp://rabbitmq");
  const channel = await conn.createChannel();
  await channel.assertQueue("user_events");
  channel.sendToQueue("user_events", Buffer.from(JSON.stringify(user)));
}

Step 5: Scaling Microservices

Horizontal scaling

docker-compose up --scale user-service=4

Now, 4 containers of the same service handle requests

Best Practices

Real Business Examples