Question 1

What is system design?

Accepted Answer

System design is the process of defining the architecture, components, data flows, and interfaces of a software system to satisfy specified requirements. In interviews, you're asked to design large-scale distributed systems like URL shorteners, social media feeds, or payment processors. Key concepts include load balancing, caching, databases, message queues, CDNs, and horizontal scaling.

Question 2

How do I prepare for system design interviews?

Accepted Answer

To prepare for system design interviews: (1) Learn core distributed systems concepts — load balancers, caches, databases, message queues, CDNs, rate limiters. (2) Practice designing systems on a canvas with components. (3) Work through real FAANG interview problems like URL shortener, rate limiter, Twitter feed, and Uber matching. (4) Solve daily mini-puzzles to build intuition. (5) Study expert solutions and understand tradeoffs. The System Bible offers all of this in one free interactive platform.

Question 3

What are common system design interview questions?

Accepted Answer

The most common system design interview questions asked at FAANG companies include: Design a URL shortener (like bit.ly), Design a rate limiter, Design a Twitter or Instagram feed, Design a ride-sharing system (like Uber), Design a messaging app (like WhatsApp or Slack), Design a video streaming service (like YouTube or Netflix), Design a file storage system (like Dropbox or Google Drive), Design a payment system (like Stripe), Design a search engine (like Google), and Design an e-commerce checkout (like Amazon).

Question 4

How do you design a URL shortener system?

Accepted Answer

A URL shortener system design includes: (1) A hash or counter-based ID generator to create short codes (e.g., base62 encoding). (2) A database (SQL or NoSQL) to map short codes to original URLs with TTL. (3) A cache layer (Redis) to serve high-read traffic without hitting the database on every redirect. (4) A load balancer to distribute traffic across multiple API servers. (5) A CDN to reduce latency for global users. (6) Analytics storage for click tracking. At scale, this handles billions of redirects with sub-10ms latency.

Question 5

What is a rate limiter in system design?

Accepted Answer

A rate limiter controls how frequently users or services can make requests to an API or resource. Common algorithms include: Token Bucket (allows bursting), Leaky Bucket (smooth output rate), Fixed Window Counter, Sliding Window Log, and Sliding Window Counter. In practice, rate limiters use Redis for distributed state, returning 429 Too Many Requests when limits are exceeded. They protect systems from abuse, DoS attacks, and ensure fair usage.

Question 6

What is caching in system design?

Accepted Answer

Caching stores frequently accessed data in fast memory to reduce database load and latency. Common caching strategies include: Cache-aside (read from cache, miss then read DB + populate cache), Write-through (write to cache and DB simultaneously), Write-behind (write to cache, async write to DB), and Read-through. Popular cache solutions are Redis and Memcached. Cache invalidation is the hardest problem — strategies include TTL expiration, event-driven invalidation, and versioning.

Question 7

What is load balancing in system design?

Accepted Answer

A load balancer distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed. Load balancing algorithms include Round Robin, Least Connections, IP Hash, and Weighted Round Robin. Load balancers operate at Layer 4 (TCP/UDP) or Layer 7 (HTTP/HTTPS). They also provide health checking, SSL termination, and sticky sessions. Examples include AWS ALB/NLB, NGINX, HAProxy, and Google Cloud Load Balancing.

Question 8

What are the key distributed systems concepts for system design interviews?

Accepted Answer

Key distributed systems concepts for interviews: CAP Theorem (Consistency, Availability, Partition tolerance), Database types (SQL vs NoSQL), Sharding and partitioning, Replication (leader-follower, multi-master), Consistent hashing, Load balancing algorithms, Caching strategies (Redis, Memcached), Message queues (Kafka, RabbitMQ, SQS), CDNs (Cloudflare, Akamai), Rate limiting, API gateways, Service discovery and mesh, Microservices vs monolith, Event sourcing and CQRS.

Question 9

How long does it take to prepare for system design interviews?

Accepted Answer

Most engineers spend 4–8 weeks preparing for system design interviews, dedicating 1–2 hours per day. A structured 30-day plan covering 1 problem per day with concept study is highly effective. Engineers with distributed systems experience may need only 2–3 weeks. The key is deliberate practice: design on a canvas, review expert solutions, and study tradeoffs — not just reading. The System Bible's 30-day practice plan covers all 15 core FAANG problems with spaced repetition.

Question 10

What is the difference between SQL and NoSQL databases in system design?

Accepted Answer

SQL databases (PostgreSQL, MySQL) offer ACID transactions, structured schemas, joins, and strong consistency. Use SQL for financial data, user accounts, and relational data. NoSQL databases include: Document stores (MongoDB) for flexible schemas, Key-Value stores (Redis, DynamoDB) for fast lookups, Wide-column (Cassandra) for write-heavy time-series, and Graph DBs (Neo4j) for relationships. Use NoSQL for high write throughput, global distribution, schema flexibility, or massive scale where horizontal sharding is required.

Question 11

What is The System Bible?

Accepted Answer

The System Bible is a free interactive system design interview practice platform. It features a drag-and-drop canvas simulator where you design systems by connecting components (load balancers, databases, caches, CDNs, message queues), configure them with real metrics, and get scored. It includes 15 FAANG-style problems, daily mini-puzzles with ELO ranking, 22 distributed systems concept guides, a 30-day practice plan, and database-first design mode.

Question 12

Is The System Bible free?

Accepted Answer

Yes, The System Bible is completely free to use. Create an account to save your progress, earn ELO rankings, track streaks, unlock achievements, and access the full 30-day practice plan. There is no paywall for any core features.