Backend from First Principles

Welcome to the Backend from First Principles documentation repository!

This repository contains a comprehensive collection of notes, code snippets, and explanations covering fundamental and advanced concepts in backend engineering. The goal of this series is to break down complex backend topics into understandable, foundational principles.

Table of Contents

The documentation is organized into the following topics:

1. HTTP and CORS - Understanding the web's foundational protocol and Cross-Origin Resource Sharing.
2. Routing in Backend - How requests are directed to the appropriate handlers.
3. Serialization and Deserialization - Converting data structures to/from formats like JSON and Protobuf.
4. Authentication and Authorization - Securing applications and managing user access.
5. Validations and Transformations - Ensuring data integrity and sanitization.
6. Controllers, Services, Repositories, and Middlewares - Exploring the layered architectural pattern and request context.
7. API Design (REST API) - Best practices for designing intuitive and scalable RESTful APIs.
8. Databases - Core concepts of database integration in backend systems.
9. Caching - The secret behind blazingly fast applications (Redis, Memcached, etc.).
10. Task Queues and Background Jobs - Managing asynchronous workloads.
11. Full-Text Search - Building fast search functionality using Elasticsearch.
12. Error Handling and Fault-Tolerant Systems - Building resilient applications that handle failures gracefully.
13. gRPC and Inter-Service Communication - Efficient communication protocols for microservices.
14. Production-Grade Configuration Management - Managing environment variables and configurations securely.
15. Logging, Monitoring, and Observability - Keeping track of system health and debugging issues in production.
16. Graceful Shutdown - Safely terminating applications without losing data or interrupting requests.
17. Backend Security - Everything you need to know to secure your backend (SQL injection, XSS, CSRF, etc.).
18. Backend Scaling and Performance Engineering (Part 1) - Strategies for scaling applications vertically and horizontally.
19. Backend Scaling and Performance Engineering (Part 2) - Advanced scaling techniques.
20. Concurrency & Parallelism - Understanding IO-bound vs CPU-bound tasks and how to optimize them.
21. Containerization, Deployment, Docker, Kubernetes, and CI/CD - Packaging and shipping applications consistently.
22. Automated Testing - Writing effective Unit, Integration, and End-to-End (E2E) tests.
23. Message Brokers and Event Streaming - Using tools like Kafka for event-driven architectures.
24. WebSockets and Real-Time Communication - Building real-time features using WebSockets.
25. OpenAPI Specification - Defining machine-readable API contracts and generating documentation, tests, and clients.
26. AI Agents and Loop Engineering - Building bounded LangGraph agents with tools, workflows, and backend integration.
27. URL Shortener System Design (HLD & LLD) - Building a scalable URL shortener from first principles. Master distributed ID generation, hot key caching, and handling millions of redirects per second.

Getting Started

Feel free to browse through the directories to explore specific topics. Each directory contains detailed markdown notes, code examples, and practical implementations.

Install as an App (PWA)

The live site is a Progressive Web App. In Chrome, Edge, or Safari you can use Install app / Add to Home Screen to pin it to your launcher or dock. Visited pages stay available offline after the first load; the service worker refreshes HTML from the network when you are online so chapter updates still show up.

Reading It Offline

Prefer a local window to a browser tab? The site can also open as an app of its own on your machine - no address bar, no tabs, its own icon in the taskbar.

npm install
npm run desktop

That builds the site, serves it locally, and opens it in app mode using the first Chromium browser it finds - Chrome, then Brave, then Edge. There is nothing extra to install. The terminal is handed straight back, and closing the window is what stops it. To pick a browser yourself, pass it: npm run desktop --edge. On a machine with only Firefox or Safari it opens in an ordinary tab instead, since neither has an app mode to borrow.

Your theme and chapter progress are kept in the app's own profile, so they start fresh rather than carrying over from the website. This local desktop flow is separate from installing the hosted PWA.

Contributing & Community

Backend from First Principles is created and maintained by @DsThakurRawat as an open engineering reference for everyone.

Contributions are warmly welcomed! You can help by: - Adding code implementations in other languages (Rust, Java, C++, TypeScript, etc.) - Improving explanations, adding architectural diagrams, or clarifying edge cases - Fixing typos, broken links, or syntax issues

Feel free to open an Issue or submit a Pull Request!

"Learn the fundamentals, and the frameworks become obvious."

Curated with dedication by @DsThakurRawat