Realistic questions for junior/mid roles:
URL Shortener: Create short redirect links. Focus on: database schema, handling collisions, caching popular links.
Simple Notes App: Create and retrieve notes. Focus on: API design, database schema, authentication basics.
Simple Chat App: Real-time messaging. Focus on: WebSockets vs polling, storing messages.
File Upload Service: Handle large files. Focus on: chunking, storage options, progress tracking.
For each question:
- Start with the simplest solution
- Then discuss how you'd scale it
- Admit what you don't know
For deeper practice, see the System Design roadmap.