Start here
Learn the basic ideas of system design, with their good and bad sides.
Learn system design by following one request.
24 Topics14 Solutions9 Diagrams
Topics
Learn one system idea at a time.
Start here
Study guide
Pick what to study based on how much time you have before the interview.
Interview approach
Four steps to lead an open design interview, from needs to scaling.
Trade-offs
Performance vs scalability
Tell apart a system slow for one user from one slow under heavy use.
Latency vs throughput
Balance the time one task takes against how many tasks finish over time.
Availability vs consistency
When the network fails, choose between the latest data and always answering.
Consistency patterns
Choose how copies of the same data stay in step for readers.
Availability patterns
Keep a service running when a server fails, using fail-over and copies.
Building blocks
Domain name system
Turn a domain name into the IP address of a server.
In the diagram: Hero diagram › ClientIn the diagram: Design Mint.com › DNSIn the diagram: Design Pastebin.com (or Bit.ly) › DNSIn the diagram: Design a key-value cache to save the results of the most recent web server queries › DNSIn the diagram: Design Amazon's sales rank by category feature › DNSIn the diagram: Design a system that scales to millions of users on AWS › DNSIn the diagram: Design the data structures for a social network › DNSIn the diagram: Design the Twitter timeline and search › ClientIn the diagram: Design a web crawler › Client
Content delivery network
Serve files from servers close to the user.
In the diagram: Hero diagram › CDNIn the diagram: Design Mint.com › CDNIn the diagram: Design Pastebin.com (or Bit.ly) › CDNIn the diagram: Design Amazon's sales rank by category feature › CDNIn the diagram: Design a system that scales to millions of users on AWS › CDNIn the diagram: Design the Twitter timeline and search › CDN
Load balancer
Share incoming requests across many servers.
In the diagram: Hero diagram › Load BalancerIn the diagram: Design Mint.com › Load BalancerIn the diagram: Design Pastebin.com (or Bit.ly) › Load BalancerIn the diagram: Design a key-value cache to save the results of the most recent web server queries › Load BalancerIn the diagram: Design Amazon's sales rank by category feature › Load BalancerIn the diagram: Design a system that scales to millions of users on AWS › Load BalancerIn the diagram: Design the data structures for a social network › Load BalancerIn the diagram: Design the Twitter timeline and search › Load BalancerIn the diagram: Design a web crawler › Load Balancer
Reverse proxy
One public front door for your internal servers.
In the diagram: Hero diagram › Web ServerIn the diagram: Design Mint.com › Web ServerIn the diagram: Design Pastebin.com (or Bit.ly) › Web ServerIn the diagram: Design a key-value cache to save the results of the most recent web server queries › Web ServerIn the diagram: Design Amazon's sales rank by category feature › Web ServerIn the diagram: Design a system that scales to millions of users on AWS › Web ServerIn the diagram: Design the data structures for a social network › Web ServerIn the diagram: Design the Twitter timeline and search › Web ServerIn the diagram: Design a web crawler › Web Server
Application layer
Run your app's logic on its own servers, apart from the web servers.
In the diagram: Hero diagram › Write APIIn the diagram: Design Mint.com › Accounts APIIn the diagram: Design Pastebin.com (or Bit.ly) › Write APIIn the diagram: Design a key-value cache to save the results of the most recent web server queries › Query APIIn the diagram: Design Amazon's sales rank by category feature › Sales APIIn the diagram: Design the data structures for a social network › Lookup ServiceIn the diagram: Design the Twitter timeline and search › Read API
Database
Where data is stored, and ways to make it handle more load.
In the diagram: Hero diagram › NoSQLIn the diagram: Design Mint.com › SQL Write Master–SlaveIn the diagram: Design Pastebin.com (or Bit.ly) › SQL Write Master–SlaveIn the diagram: Design a key-value cache to save the results of the most recent web server queries › Reverse Index ServiceIn the diagram: Design Amazon's sales rank by category feature › SQL Write Master–SlaveIn the diagram: Design a system that scales to millions of users on AWS › NoSQLIn the diagram: Design the data structures for a social network › Person ServerIn the diagram: Design the Twitter timeline and search › SQL Read ReplicasIn the diagram: Design a web crawler › Crawler Service
Cache
Keep earlier results so repeat requests are fast and servers do less work.
In the diagram: Hero diagram › Memory CacheIn the diagram: Design Mint.com › Read APIIn the diagram: Design Pastebin.com (or Bit.ly) › Memory CacheIn the diagram: Design a key-value cache to save the results of the most recent web server queries › Memory CacheIn the diagram: Design Amazon's sales rank by category feature › Memory CacheIn the diagram: Design a system that scales to millions of users on AWS › Memory CacheIn the diagram: Design the data structures for a social network › Memory CacheIn the diagram: Design the Twitter timeline and search › Tweet Info ServiceIn the diagram: Design a web crawler › Document Service
Asynchronism
Do slow work in the background, not while the user waits.
In the diagram: Hero diagram › Worker ServiceIn the diagram: Design Mint.com › Notification ServiceIn the diagram: Design a system that scales to millions of users on AWS › Worker ServiceIn the diagram: Design the Twitter timeline and search › Notification ServiceIn the diagram: Design a web crawler › Reverse index queue
Communication
Ways that clients and servers send data to each other.
In the diagram: Design Mint.com › ClientIn the diagram: Design a key-value cache to save the results of the most recent web server queries › ClientIn the diagram: Design Amazon's sales rank by category feature › ClientIn the diagram: Design a system that scales to millions of users on AWS › ClientIn the diagram: Design the data structures for a social network › ClientIn the diagram: Design a web crawler › Query API
Security
Basic steps to protect data and user input.
Reference
Powers of two table
A table of powers of two and the sizes they give.
Latency numbers
Typical times of common computer actions, for quick rough sums.
Additional interview questions
More design interview questions, each with links to help you solve it.
Real world architectures
Articles on how real systems are built.
Company architectures
Links to how named companies built their systems.
Company engineering blogs
Engineering blogs from many companies, for interview prep.
Solutions
See the ideas in use.
System design
Design Mint.com
Design a service that links bank accounts, reads transactions, and suggests a budget.
Design Pastebin.com (or Bit.ly)
Design a site where users paste text and share it through a random link.
Design a key-value cache to save the results of the most recent web server queries
Design a cache that saves the results of the latest web server searches.
Design Amazon's sales rank by category feature
Design a feature that ranks the past week's best-selling products by category.
Design a system that scales to millions of users on AWS
Design a service that grows from one user to millions of users on AWS.
Design the data structures for a social network
Design the data for a social network that finds the shortest path between people.
Design the Twitter timeline and search
Design a Twitter timeline and search: post tweets, view timelines, search keywords.
Design a web crawler
Design a crawler that visits web pages and lets users search what it found.
Object-oriented design
Design a call center
Design the code for a call center with operators, supervisors and directors.
Design a deck of cards
Design the code for a 52-card deck, then extend it for blackjack.
Design a hash map
Design a hash map, a key lookup table that handles clashing keys by chaining.
Design an LRU cache
Design a cache for web query results that drops the least recently used items.
Design an online chat
Design a text chat with users, friend lists, and group chats.
Design a parking lot
Design a multi-level parking lot for motorcycles, cars and buses.
Diagrams
Explore the visual guides.
How a web system scales
Walk through the main parts of a web system.
Design Mint.com
Design Pastebin.com (or Bit.ly)
Design a key-value cache to save the results of the most recent web server queries
Design Amazon's sales rank by category feature
Design a system that scales to millions of users on AWS
Design the data structures for a social network
Design the Twitter timeline and search
Design a web crawler
Images from the primer
The System Design Primer
Shown in: Design a system that scales to millions of users on AWS
Anki flashcards
Shown in: the original README
Coding Resource: Interactive Coding Challenges
Shown in: the original README
Index of system design topics
Shown in: Design the Twitter timeline and search
Imgur
Shown in: Design the data structures for a social network
Imgur
Shown in: Design a key-value cache to save the results of the most recent web server queries
Imgur
Shown in: Design Amazon's sales rank by category feature
CAP theorem
Shown in: Availability vs consistency › CAP theorem
Domain name system
Shown in: Domain name system › Domain name system
Content delivery network
Shown in: Content delivery network › Content delivery network
Load balancer
Shown in: Load balancer › Load balancer
Reverse proxy (web server)
Shown in: Reverse proxy › Reverse proxy (web server)
Application layer
Shown in: Application layer › Application layer
Database
Shown in: Database › Database
Master-slave replication
Shown in: Database › Master-slave replication
Master-master replication
Shown in: Database › Master-master replication
Federation
Shown in: Database › Federation
Sharding
Shown in: Database › Sharding
Wide column store
Shown in: Database › Wide column store
Graph database
Shown in: Database › Graph database
SQL or NoSQL
Shown in: Database › SQL or NoSQL
Cache-aside
Shown in: Cache › Cache-aside
Write-through
Shown in: Cache › Write-through
Write-behind (write-back)
Shown in: Cache › Write-behind (write-back)
Refresh-ahead
Shown in: Cache › Refresh-ahead
Asynchronism
Shown in: Asynchronism › Asynchronism
Communication
Shown in: Communication › Communication
Transmission control protocol (TCP)
Shown in: Communication › Transmission control protocol (TCP)
User datagram protocol (UDP)
Shown in: Communication › User datagram protocol (UDP)
Remote procedure call (RPC)
Shown in: Communication › Remote procedure call (RPC)
Real world architectures
Shown in: Real world architectures › Real world architectures