System Design

Fundamentals

• Scalability (Horizontal vs Vertical)
• CAP Theorem
• Consistency Patterns
• Availability Patterns
• Load Balancing
• Caching Strategies
• Content Delivery Networks
• DNS & Domain Resolution

Data Layer

• SQL vs NoSQL
• Database Sharding
• Database Replication
• Indexing Strategies
• Data Partitioning

Communication

• REST vs gRPC vs GraphQL
• Message Queues (Kafka, RabbitMQ)
• WebSockets & Real-Time Communication
• API Gateway Pattern

Infrastructure

• Microservices Architecture
• Rate Limiting
• Circuit Breaker Pattern
• Observability (Logs, Metrics, Traces)
• Containers & Orchestration

Interview deep-dives

• Back-of-envelope numbers: the constants, the four calculations, the thresholds that turn a number into a decision, and worked chargeback, PIX and authorisation prompts
• Nubank lead system design study notes — Nubank’s prep document decoded (numbers, v1 → v2 → v3, degradation, security, six-day plan), the Hello Interview method they recommend mapped onto the hour, chargebacks, chargeback mock interview, ledger, and pivot prompts (authoriser, credit limit, fraud, PIX, ride-hailing, ad clicks)

Classic Design Problems

• Design: URL Shortener
• Design: Rate Limiter
• Design: Chat System
• Design: News Feed
• Design: Notification System
• Design: Distributed Cache
• Design: Search Autocomplete

Framework

System Design Interview Framework

1. Clarify requirements (functional + non-functional)
2. Back-of-envelope estimation (QPS, storage, bandwidth): see Back-of-Envelope Numbers
3. High-level design (API + data model + architecture diagram)
4. Deep dive (pick 2-3 components to detail)
5. Bottlenecks & trade-offs (what breaks at 10x scale?)