### 🏗️ 1. High-Level System Architecture - **Tech Stack:** - **Frontend:** Next.js (React), Tailwind CSS, TypeScript - **Backend:** Node.js (Express) or Go microservices - **Database:** PostgreSQL (Primary ACID Data) + Redis (Session/Caching) - **Storage:** Amazon S3 / Cloudflare R2 (Video & Media assets) - **Architecture Pattern:** **Modular Monolith** to handle up to 50k active users efficiently without microservices complexity. --- ### 🗄️ 2. Database Schema & Data Model - **Core Entities:** `Users`, `Courses`, `Enrollments`, `Payments`, `Lessons` - **Data Model (PostgreSQL Example):** - `Users` (id, email, password_hash, role: student/instructor, created_at) - `Courses` (id, instructor_id, title, price, status: draft/published) - `Enrollments` (id, user_id, course_id, enrolled_at, progress_pct) --- ### 🔌 3. RESTful API Specifications - **POST `/api/v1/auth/register`** -> Create a new student/instructor account. - **GET `/api/v1/courses`** -> Fetch paginated course catalog with Redis caching. - **POST `/api/v1/enrollments`** -> Process enrollment via Stripe webhook integration. --- ### ⚡ 4. Scalability, Security & Performance - **Caching:** Cache course metadata in Redis (`TTL: 1 hour`) to reduce DB load. - **Security:** JWT authentication via HTTP-only cookies, Stripe for PCI-compliant payment handling, and AWS CloudFront for video CDN streaming. - **Rate Limiting:** Express-rate-limit set to 100 requests per 15 minutes per IP. --- ### ⚠️ 5. Edge Cases & Technical Risks - **Risk:** High concurrent streaming during peak hours. - **Mitigation:** Offload video streaming completely to Cloudflare Stream / AWS CloudFront.