1️⃣ Generic Thought Process for High-Scale System Design
Whenever you get a “big scale” question, break your answer into six pillars so you don’t miss anything:
A. Requirements & Constraints
- Functional vs. non-functional requirements
- Traffic estimates: QPS (queries per second), peak load, growth
- Data volume, read/write ratio, latency requirements
B. High-Level Architecture
- Separate into frontend, backend, database, caching, and async processing layers
- Use load balancers and CDNs for distribution
C. Scaling & Performance
- Horizontal scaling for stateless services (Kubernetes, Auto-scaling)
- Database sharding/partitioning, replication
- Caching (Redis, Memcached) for hot data
- Queue-based async processing for heavy workloads
D. Data Storage Strategy
- SQL vs. NoSQL (based on ACID vs. scalability needs)
- Indexing strategy, denormalization for reads
- Data retention & archival for huge datasets
E. Security & Authentication
- OAuth2/OpenID Connect for API auth
- HTTPS everywhere
- Input validation, rate limiting, and request throttling
- PCI DSS compliance for payment-like systems
F. Monitoring & Reliability
- Logging (ELK stack, Splunk)
- Metrics (Prometheus, Grafana)
- Alerts & auto-healing strategies
2️⃣ Generic Big-Scale System Design Questions
Database
- How would you design a database that can handle 1M+ concurrent users?
- How would you design a schema for storing billions of transactions?
- What is your approach to database partitioning/sharding?
- How do you handle read-heavy workloads efficiently?
- How would you ensure ACID compliance in a distributed database setup?
Backend
- How do you design a stateless service that can scale horizontally?
- How would you process millions of requests per minute?
- How would you implement asynchronous data processing for heavy workloads?
- How do you design APIs that can handle high traffic without breaking?
Frontend
- How do you design a frontend that can load fast for millions of users globally?
- How would you cache static assets efficiently?
- How do you handle real-time updates (e.g., WebSockets, SSE, polling)?
Scaling
- How would you scale a service from 1K users to 1M users?
- How do you design for peak loads (e.g., Black Friday traffic spikes)?
- How would you balance load across multiple regions?
- How would you handle a sudden traffic spike 10x higher than normal?
Authentication & Authorization
- How would you design authentication for millions of users without performance bottlenecks?
- How do you handle session management in a distributed system?
- How would you implement role-based access control at scale?
Security
- How do you secure APIs against brute-force and DDoS attacks?
- How do you protect sensitive data in transit and at rest?
- How do you design an audit logging system for security compliance?
Reliability
- How would you design a system with 99.99% uptime?
- How do you ensure zero downtime deployments?
- How would you handle failover if a whole region goes down?