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added advanced backend topics
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‎backend_with_node.js/000.advanced_backend.md

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# 1. Securing APIs
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## a) Authentication
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- **Basic Authentication** (username:password) — important for internal APIs.
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- **OAuth 2.0** — learn **Authorization Code flow**, **Client Credentials flow**, and **PKCE**.
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- **JWT (JSON Web Token)** — token-based authentication.
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- **OpenID Connect** — an identity layer on top of OAuth 2.0 (important for login systems).
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- **Multi-Factor Authentication (MFA)** — adding OTPs, apps like Google Authenticator.
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- **Biometric Authentication** — integrating with FaceID/Fingerprint APIs (optional but good for mobile-first apps).
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- **SSO (Single Sign-On)** — via OAuth/SAML (very important for enterprise backend apps).
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- **Session Management** — cookie-based authentication vs. token-based sessions.
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## b) Authorization
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- **RBAC (Role-Based Access Control)** — define roles like Admin, User, Guest.
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- **ABAC (Attribute-Based Access Control)** — based on attributes (e.g., department, age).
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- **PBAC (Policy-Based Access Control)** — newer — think fine-grained control using policies.
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- **Scope Management** — in OAuth 2.0 (limiting what a token can do).
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- **API Gateway Authorization** — secure APIs with API Gateways like **AWS API Gateway**, **Kong**, or **Apigee**.
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---
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# 2. Performance Optimization
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## a) Caching strategies
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- **Redis caching** — store sessions, API responses, database query results.
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- **Memory caching (Node.js)** — simple in-memory cache for ultra-fast reads.
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- **CDN caching** — for static assets (Cloudflare, AWS CloudFront).
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- **Cache Invalidation** strategies (very important):
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- TTL (Time to Live)
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- Manual Purging
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- Stale-While-Revalidate (used in Next.js)
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## b) API Rate Limiting
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- **express-rate-limit** library (Node.js).
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- **Redis-backed rate limiters** (for distributed systems).
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- **Token Bucket** and **Leaky Bucket** algorithms (understand how they work).
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- **Global API Gateways** (e.g., AWS API Gateway's throttling).
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## c) Query Optimization and Database Indexing
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- **Proper database indexing** (single field, composite indexes, partial indexes).
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- **Query Optimization Techniques**:
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- Avoid SELECT \* (only fetch needed fields).
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- Query planning and `EXPLAIN` command for databases.
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- Using **pagination** instead of fetching all records.
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- **Caching database queries** where necessary.
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- **Connection Pooling** — reusing DB connections instead of opening new ones.
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- **Database sharding and replication** — advanced for high scale.
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---
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# 3. Testing APIs and Microservices
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## a) Unit Testing
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- **Mocha** + **Chai** (most common in Node.js world).
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- **Jest** (modern and more powerful for new projects).
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- **Sinon** for mocking external services.
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## b) Integration and End-to-End Testing
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- **Supertest** — for API endpoint testing directly in Node.
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- **Postman/Newman** — create full testing collections.
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- **Pact** — for **Contract Testing** between microservices.
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- **Cypress** — for full-stack E2E tests if your backend interacts heavily with UI.
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## c) Test Automation & CI/CD
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- **GitHub Actions**, **GitLab CI/CD**, **CircleCI** — run API tests automatically on push.
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- **Mock Servers** — simulate 3rd party APIs when testing your API (Postman Mock Server, WireMock).
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---
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# 4. Deployment and Scaling
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## a) Deployment
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- **Deploy on AWS EC2**, **AWS Elastic Beanstalk**, **Google App Engine**, **Heroku**, **Render**, or **Vercel**.
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- **PM2** — process manager for Node.js to handle auto-restarts and scaling.
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- **Environment Variables** handling (dotenv, Vault, AWS Secrets Manager).
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## b) Scaling
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- **Docker** — containerize your Node.js apps.
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- **Kubernetes (K8s)** — orchestrate and scale containers automatically.
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- **Service Mesh** (Istio/Linkerd) — advanced networking for microservices.
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- **Horizontal Pod Autoscaling** (HPA) — Kubernetes automatically adding/removing pods.
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- **Vertical Scaling** (adding more power to a server) vs. **Horizontal Scaling** (adding more servers).
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- **Load Balancers** (AWS ALB, Nginx, HAProxy) to distribute traffic.
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- **Stateless APIs** — APIs should not store any state locally if you want to scale horizontally.
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## c) Serverless
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- **AWS Lambda**, **Google Cloud Functions** — event-driven, pay-per-use backend functions.
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- **Serverless Framework** — tool for managing serverless apps.
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## d) Microservices-specific scaling
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- **Distributed Tracing** (Jaeger, Zipkin) — track requests across multiple services.
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- **Event-Driven Architecture** — using Kafka, RabbitMQ, or SQS for communication.
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---
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# Additional must-know related topics
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- **API Documentation Standards**
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- OpenAPI Specification (Swagger UI)
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- Redoc
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- **GraphQL APIs** — alternative to REST, learn **Apollo Server** and **Federation**.
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- **WebSockets** for real-time APIs (Socket.IO, native WS module).
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- **Event Sourcing and CQRS** — design patterns for complex backend systems.
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- **Monitoring and Observability**
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- Prometheus + Grafana (metrics monitoring)
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- ELK Stack (Elasticsearch, Logstash, Kibana) for logging
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- **Security Best Practices**
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- OWASP Top 10 for APIs
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- Helmet.js (HTTP security headers)
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- Proper input sanitization (SQL injection, XSS prevention)
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- **API Gateway Concepts**
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- Kong
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- AWS API Gateway
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- NGINX as an API Gateway
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- **Versioning your APIs**
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- URI Versioning (`/api/v1/resource`)
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- Header Versioning
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- **Message Queues and Pub/Sub systems**
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- RabbitMQ
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- Apache Kafka
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- AWS SNS/SQS
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- **Domain-Driven Design (DDD)** — high-level API and microservices design thinking.
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- **Resiliency Patterns**
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- Circuit Breaker (with libraries like `opossum` in Node.js)
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- Retry Logic
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- Bulkhead Isolation
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---
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# Summary Table
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| Area | Topics to Learn |
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| :--------------------- | :---------------------------------------------------------------- |
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| **Security** | OAuth 2.0, JWT, MFA, OpenID Connect, RBAC, ABAC |
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| **Performance** | Redis caching, API Rate Limiting, Query Optimization, DB Indexing |
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| **Testing** | Unit + Integration + Contract Testing, Automation |
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| **Deployment/Scaling** | Docker, Kubernetes, Serverless, Monitoring, Microservices scaling |
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| **Modern Skills** | GraphQL, WebSockets, Event-Driven Systems, Resiliency Patterns |
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---

‎redis/node_server/app.js

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const express = require("express");
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const axios = require("axios");
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const Redis = require("ioredis");
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const app = express();
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const redis = new Redis({ host: "localhost", port: 6379 }); // Redis Docker container
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const PORT = 3000;
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// Example API to cache (we'll use JSONPlaceholder)
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const API_URL = "https://jsonplaceholder.typicode.com/posts";
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// Cache middleware
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async function cacheMiddleware(req, res, next) {
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const { id } = req.params;
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const cacheKey = `post:${id}`;
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try {
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// Check Redis for cached data
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const cachedData = await redis.get(cacheKey);
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if (cachedData) {
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console.log("Serving from cache 🚀");
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return res.send(JSON.parse(cachedData));
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}
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next(); // No cache → proceed to fetch
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} catch (err) {
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console.error("Cache error:", err);
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next();
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}
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}
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// Route: Get a post by ID (with caching)
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app.get("/posts/:id", cacheMiddleware, async (req, res) => {
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const { id } = req.params;
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const cacheKey = `post:${id}`;
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try {
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// Fetch from API
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const response = await axios.get(`${API_URL}/${id}`);
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const data = response.data;
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// Save to Redis (expire after 1 hour = 3600 seconds)
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await redis.setex(cacheKey, 600, JSON.stringify(data));
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console.log("Serving from API ⚡");
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res.send(data);
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} catch (err) {
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res.status(500).send("Error fetching post");
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}
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});
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app.listen(PORT, () => {
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console.log(`Server running on http://localhost:${PORT}`);
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});

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