scalable-api-design.md

Building Scalable and Maintainable Systems

1. API Design

RESTful vs GraphQL APIs

• RESTful APIs: Follows a structured approach with endpoints for each resource (e.g., /users, /posts).
• GraphQL APIs: Allows fetching only required data in a single request, reducing over-fetching and under-fetching.

Example: RESTful API with Express

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

app.get('/users/:id', (req, res) => {
    res.json({ id: req.params.id, name: "Pisey" });
});

app.listen(3000, () => console.log('Server running on port 3000'));

Example: GraphQL API with Apollo Server

const { ApolloServer, gql } = require('apollo-server');

const typeDefs = gql`
  type User {
    id: ID!
    name: String!
  }
  type Query {
    user(id: ID!): User
  }
`;
const resolvers = {
  Query: {
    user: (_, { id }) => ({ id, name: "Pisey" }),
  },
};
const server = new ApolloServer({ typeDefs, resolvers });
server.listen().then(({ url }) => console.log(`Server running at ${url}`));

---

2. Authentication & Authorization

JWT-based Authentication with Passport.js

const passport = require('passport');
const JwtStrategy = require('passport-jwt').Strategy;
const ExtractJwt = require('passport-jwt').ExtractJwt;
const opts = {
  jwtFromRequest: ExtractJwt.fromAuthHeaderAsBearerToken(),
  secretOrKey: 'your_secret_key',
};

passport.use(new JwtStrategy(opts, (jwt_payload, done) => {
  if (jwt_payload.id) return done(null, jwt_payload);
  return done(null, false);
}));

---

3. Error Handling

Using Middleware for Error Handling

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).json({ message: 'Internal Server Error' });
});

---

4. Caching with Redis

Installing and Connecting Redis

npm install redis

const redis = require('redis');
const client = redis.createClient();
client.on('error', (err) => console.error('Redis error:', err));

// Caching middleware
const cacheMiddleware = (req, res, next) => {
  const key = `user:${req.params.id}`;
  client.get(key, (err, data) => {
    if (data) return res.json(JSON.parse(data));
    next();
  });
};

---

5. Testing

Writing Unit Tests with Jest

npm install --save-dev jest

test('adds 1 + 2 to equal 3', () => {
  expect(1 + 2).toBe(3);
});

Integration Testing with Supertest

npm install --save-dev supertest

const request = require('supertest');
const app = require('../app');

test('GET /users', async () => {
  const res = await request(app).get('/users/1');
  expect(res.statusCode).toBe(200);
  expect(res.body).toHaveProperty('name');
});