201 Free System Design Lessons to Crack SDE Interviews in 2027

Published September 2026 · avivashishta.com

You commented design, so here are all 201 lessons, free, with a link for each. They come from two GitHub repos, and I checked every link on 27 September 2026 and dropped the dead ones. A "lesson" here is one page, video, solved problem or paper you can finish in one sitting. No paid books or courses.

The short version: 80 lessons from the System Design Primer (topic chapters plus 14 solved problems) and 121 from Awesome System Design Resources (concepts, 43 interview problems, engineering blogs and the classic papers). Follow the 4-week plan, then use the rest as a reference.

The two repos

donnemartin/system-design-primer ~372K ★

github.com/donnemartin/system-design-primer

One long, well-organised guide with trade-offs for every topic, plus solved interview problems with diagrams and object-oriented design solutions in notebooks.

ashishps1/awesome-system-design-resources ~41.8K ★

github.com/ashishps1/awesome-system-design-resources

A curated list: short concept lessons (mostly AlgoMaster), interview problems by difficulty (many are YouTube walkthroughs), real engineering blogs and must-read papers.

The 4-week plan I'd follow

  1. Week 1: foundations: System design primer "Start here", then the Core Concepts and Networking lessons (scalability, CAP, DNS, load balancing).
  2. Week 2: data: Database and Caching lessons: indexing, sharding, replication, cache strategies, CDNs.
  3. Week 3: patterns: Async communication, microservices, trade-offs. Read the Discord and Slack engineering posts.
  4. Week 4: problems: Do the answering framework, then 2 Easy, 2 Medium and 1 Hard problem out loud, with a timer.

Part 1: System Design Primer (80 lessons)

Start here (2)

  1. Study guide (short, medium and long interview timelines)
  2. How to approach a system design interview question

Topic chapters (64)

  1. System design topics: start here: Step 1: Review the scalability video lecture
  2. System design topics: start here: Step 2: Review the scalability article
  3. Performance vs scalability
  4. Latency vs throughput
  5. Availability vs consistency
  6. Availability vs consistency: CAP theorem
  7. Consistency patterns
  8. Consistency patterns: Weak consistency
  9. Consistency patterns: Eventual consistency
  10. Consistency patterns: Strong consistency
  11. Availability patterns
  12. Availability patterns: Fail-over
  13. Availability patterns: Replication
  14. Availability patterns: Availability in numbers
  15. Domain name system
  16. Content delivery network
  17. Content delivery network: Push CDNs
  18. Content delivery network: Pull CDNs
  19. Load balancer
  20. Load balancer: Active-passive
  21. Load balancer: Active-active
  22. Load balancer: Layer 4 load balancing
  23. Load balancer: Layer 7 load balancing
  24. Load balancer: Horizontal scaling
  25. Reverse proxy (web server)
  26. Reverse proxy (web server): Load balancer vs reverse proxy
  27. Application layer
  28. Application layer: Microservices
  29. Application layer: Service discovery
  30. Database
  31. Database: Relational database management system (RDBMS)
  32. Database: NoSQL
  33. Database: SQL or NoSQL
  34. Database: Federation
  35. Database: Denormalization
  36. Database: SQL tuning
  37. Cache
  38. Cache: Client caching
  39. Cache: CDN caching
  40. Cache: Web server caching
  41. Cache: Database caching
  42. Cache: Application caching
  43. Cache: Caching at the database query level
  44. Cache: Caching at the object level
  45. Cache: When to update the cache
  46. Cache: Cache-aside
  47. Cache: Write-through
  48. Cache: Write-behind (write-back)
  49. Cache: Refresh-ahead
  50. Asynchronism
  51. Asynchronism: Message queues
  52. Asynchronism: Task queues
  53. Asynchronism: Back pressure
  54. Communication
  55. Communication: Transmission control protocol (TCP)
  56. Communication: User datagram protocol (UDP)
  57. Communication: Remote procedure call (RPC)
  58. Communication: Representational state transfer (REST)
  59. Security
  60. Appendix: Powers of two table
  61. Appendix: Latency numbers every programmer should know
  62. Appendix: Additional system design interview questions
  63. Appendix: Real world architectures
  64. Appendix: Company architectures

Solved system design problems, with diagrams (8)

  1. Design Pastebin.com (or Bit.ly)
  2. Design the Twitter timeline and search
  3. Design a web crawler
  4. Design Mint.com
  5. Design the data structures for a social network
  6. Design a key-value store for a search engine
  7. Design Amazon's sales ranking by category feature
  8. Design a system that scales to millions of users on AWS

Solved object-oriented design problems, with code (6)

  1. Design a hash map
  2. Design an LRU cache
  3. Design a call center
  4. Design a deck of cards
  5. Design a parking lot
  6. Design a chat server

Part 2: Awesome System Design Resources (121 lessons)

Core Concepts (9)

  1. Scalability
  2. Availability
  3. Reliability
  4. SPOF
  5. Latency vs Throughput vs Bandwidth
  6. Consistent Hashing
  7. CAP Theorem
  8. Failover
  9. Fault Tolerance

Networking Fundamentals (8)

  1. OSI Model
  2. IP Addresses
  3. Domain Name System (DNS)
  4. Proxy vs Reverse Proxy
  5. HTTP/HTTPS
  6. TCP vs UDP
  7. Load Balancing
  8. Checksums

API Fundamentals (8)

  1. APIs
  2. API Gateway
  3. REST vs GraphQL
  4. WebSockets
  5. Webhooks
  6. Idempotency
  7. Rate limiting
  8. API Design

Database Fundamentals (8)

  1. ACID Transactions
  2. SQL vs NoSQL
  3. Database Indexes
  4. Database Sharding
  5. Data Replication
  6. Database Scaling
  7. Databases Types
  8. Bloom Filters

Caching Fundamentals (5)

  1. Caching 101
  2. Caching Strategies
  3. Cache Eviction Policies
  4. Distributed Caching
  5. Content Delivery Network (CDN)

Asynchronous Communication (3)

  1. Pub/Sub
  2. Message Queues
  3. Change Data Capture (CDC)

Distributed System and Microservices (8)

  1. HeartBeats
  2. Service Discovery
  3. Consensus Algorithms
  4. Distributed Locking
  5. Gossip Protocol
  6. Circuit Breaker
  7. Disaster Recovery
  8. Distributed Tracing

Architectural Patterns (4)

  1. Client-Server Architecture
  2. Microservices Architecture
  3. Event-Driven Architecture
  4. Peer-to-Peer (P2P) Architecture

System Design Tradeoffs (8)

  1. Top 15 Tradeoffs
  2. Vertical vs Horizontal Scaling
  3. Concurrency vs Parallelism
  4. Long Polling vs WebSockets
  5. Batch vs Stream Processing
  6. Stateful vs Stateless Design
  7. Strong vs Eventual Consistency
  8. Latency vs Throughput

Interview framework (1)

  1. How to Answer a System Design Interview Problem

System Design Interview Problems (Easy) (9)

  1. Design URL Shortener like TinyURL
  2. Design Load Balancer
  3. Design Content Delivery Network (CDN)
  4. Design Parking Garage
  5. Design Vending Machine
  6. Design Distributed Key-Value Store
  7. Design Distributed Cache
  8. Design Authentication System
  9. Design Unified Payments Interface (UPI)

System Design Interview Problems (Medium) (23)

  1. Design WhatsApp
  2. Design Spotify
  3. Design Instagram
  4. Design Notification Service
  5. Design Distributed Job Scheduler
  6. Design Tinder
  7. Design Facebook
  8. Design Twitter
  9. Design Reddit
  10. Design Netflix
  11. Design Youtube
  12. Design Google Search
  13. Design E-commerce Store like Amazon
  14. Design TikTok
  15. Design Shopify
  16. Design Airbnb
  17. Design Rate Limiter
  18. Design Distributed Message Queue like Kafka
  19. Design Flight Booking System
  20. Design Online Code Editor
  21. Design an Analytics Platform (Metrics & Logging)
  22. Design Payment System
  23. Design a Digital Wallet

System Design Interview Problems (Hard) (11)

  1. Design Location Based Service like Yelp
  2. Design Uber
  3. Design Food Delivery App like Doordash
  4. Design Google Docs
  5. Design Google Maps
  6. Design Zoom
  7. Design File Sharing System like Dropbox
  8. Design Ticket Booking System like BookMyShow
  9. Design Distributed Web Crawler
  10. Design Code Deployment System
  11. Design Distributed Locking Service

Must-Read Engineering Articles (6)

  1. How Discord stores trillions of messages
  2. Building In-Video Search at Netflix
  3. How Canva scaled Media uploads from Zero to 50 Million per Day
  4. How Airbnb avoids double payments in a Distributed Payments System
  5. Stripe's payments APIs - The first 10 years
  6. Real time messaging at Slack

Must-Read Distributed Systems Papers (10)

  1. Paxos: The Part-Time Parliament
  2. MapReduce: Simplified Data Processing on Large Clusters
  3. The Google File System
  4. Dynamo: Amazon's Highly Available Key-value Store
  5. Kafka: a Distributed Messaging System for Log Processing
  6. Spanner: Google's Globally-Distributed Database
  7. Bigtable: A Distributed Storage System for Structured Data
  8. ZooKeeper: Wait-free coordination for Internet-scale systems
  9. The Log-Structured Merge-Tree (LSM-Tree)
  10. The Chubby lock service for loosely-coupled distributed systems

How I'd use this

Want to know what else interviews test now? Read what 2027 interviews will actually ask you.

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