System design sketches for popular system design interview questions.
See the sketches in full resolution at okso.app/showcase/system-design
Social Network
Functional requirements:
------------------------
- Follow people
- See followers and falowees
- Create posts (text, image, url, @mentions)
- Like posts
- View user feed
- View home feed
Non-functional requirements:
----------------------------
- Add post <500ms
- View feed <500ms
- Post in feed with ~2 mins delay is ok
- Billions of users
- Unlimited followers
Core entities:
--------------
- User
- Follow
- Post
API (RPC-like):
---------------
- POST /getFollowers {userId}
- POST /getFollowees {userId}
- POST /followUser {userId}
- POST /createPost {text}
- POST /likePost {postId}
- POST /getHomeFeed {userId}
- POST /getUserFeed {userId}
Design sketch:
Deep dives:
- Social network: System design sketch (okso.app)
- Facebook News Feed (hellointerview)
- Instagram + Twitter + Facebook + Reddit (Jordan has no life)
Ride-Sharing App
Functional requirements:
------------------------
- Rider gets estimated fare (by Start and Destination locations)
- Rider requests a ride based on the estimate
- Driver accepts/denies request + Navigates to pickup/drop-off
Non-functional requirements:
----------------------------
- Low latency for rider-driver matching (<1min)
- Consistency of rider-driver 1:1 matching
- For one ride, only one driver will get request at a time
- Highly available outside matching
- Handle high-throughput (peak hours, popular events)
Core entities:
--------------
- Rider
- Driver
- Ride
- Location
API:
---------------
- POST /getEstimate({from, to}) --> Partial<Ride>
- POST /requestRide({ride_id}) --> Ride
- POST /getRide({ride_id})
- gets the latest ride entity to display the
ride details for both rider and driver apps
- POST /updateLocation({lat, lon})
- both driver and rider can update their locations
which may be used to display their on the map
- drivers might update their location i.e. once
per 5 seconds (it is needed for matching)
- however this can be optimised on the client side,
where we might say that location update is
proportional to driver speed: for still drivers
we update location rarely, for moving - more often
- POST /acceptRide({ride_id, accept})
- ride is being accepted by the driver
- POST /updateRide({ride_id, status})
Design sketch:
Deep dives:
- Ride-sharing platform: System design sketch (okso.app)
- Design Uber (hellointerview)
Messenger
Functional requirements:
------------------------
- Group chat (<100 users)
- Send message
- Receive message
- Persist messages (user messages are
available on multiple devices)
Non-functional requirements:
----------------------------
- Low latency for message delivery (<500ms)
- No lost messages (delivery guarantee)
Core entities:
--------------
- Users
- Groups
- Messages
API:
---------------
- createGroup({users: [], name: ''}) -> {group_id}
- joinGroup({group_id}) -> "ACK"/ "ERR"
- quitGroup({group_id}) -> "ACK"/ "ERR"
- getMyGroups() -> {groups: []}
- getGroupMessages({group_id, max_message_id, min_message_id}) -> {messages: []}
WebSocket:
- connect()
- sendMessage({group_id, message, media: []}) -> "ACK"/ "ERR"
- onGroupUpdated({group_id, participants}) -> "ACK"
- onMessage({chat_id, user_id, message, attachments}) -> "ACK"
Design sketch:
Deep dives:
- Messenger: System design sketch (okso.app)
- Facebook Messenger + WhatsApp (Jordan has no life)
- Messenger/WhatsApp Design Deep Dive (Jordan has no life)
- Design Whatsapp or Messenger (hellointerview)
Video Streaming App
Functional requirements:
------------------------
- Upload video
- Watch video (read-heavy)
- Comment on video
Non-functional requirements:
----------------------------
- Reliable uploads (no corrupted/missing videos)
- Read-heavy (read/write ratio ~100:1)
- Availability > Consistency (1-2 min delay between upload and feed is ok)
- Low latency (before video starts playing)
Core entities:
--------------
- User
- Video Metadata
- Video Chunks
- Users
- Comments
API (RPC-like):
---------------
- POST /initiateUpload {title, description, video, ...}}
- server responds with S3 private upload URL
- the actual video upload is going directly from client to S3
- GET /watch {video_id}
- returns video chunks metadata
- S3 (or CDN) URLs to manifest/playlist files
- video streaming happens directly from CDNs
- download by chunks (buffering, ~1Mb), no need to load all
Design sketch:
Deep dives:
- Video streaming platform: System design sketch (okso.app)
- Design Youtube (NeetCode)
- Netflix + YouTube (Jordan has no life)
- System Design: YouTube (System Design Fight Club)
File Hosting App
Functional requirements:
------------------------
- Upload file
- Download file
- Sync files across devices
Non-functional requirements:
----------------------------
- Availability over consistency
- Download the older version of
the file instead of waiting
for a new version to propagate
is ok
- low latency for uploads and downloads
- support large files (50Gb)
- resumable uploads
- high data integrity (accurate syncs)
Core entities:
--------------
- File (row bytes)
- File Metadata
- Users
API:
---------------
- POST /uploadFile({metadata}) --> {upload_id, presigned_url}
- POST /getFile({file_id}) --> {file{}, metadata}
- POST /getChanges({since}) --> file_metadata[]
Design sketch:
Deep dives:
- File hosting app (okso.app)
- Design Dropbox (hellointerview)
Web Crawler
Functional requirements:
------------------------
- Scrape the web starting from seed URLs
- Extract and store text data
Non-functional requirements:
----------------------------
- Fault-tolerant
- Politeness (respect robots.txt, don't DDoS)
- Scale to 1B pages
- Efficient (crawl within a week)
Core entities:
--------------
- URLs
- Text data
- Domain metadata
Interface:
----------
- input: seed URLs
- output: text data
Data Flow:
----------
1. Take seed URLs from a frontier and the IP from DNS
2. Fetch HTML
3. Extract text
4. Store text in the database
5. Extract URLs from the page and add then to the frontier
6. Repeat steps 1-5 until all URLs are crawled
Design sketch:
Deep dives:
- Web-crawler app: System design sketch (okso.app)
- Design a Web Crawler (hellointerview)
- Design a Web Crawler (Jordan has no life)
- System Design distributed web crawler (Tech Dummies Narendra)
Top comments (1)
This is so awesome!