System Design: The New Gatekeeper

As senior engineering roles become more competitive, the System Design interview has become the ultimate filter. It's no longer just about load balancers and sharding; in 2026, interviewers expect deep knowledge of event-driven architectures, real-time data processing, and AI-native infrastructure.

The Top 5 Questions You Must Master

1. Design a Real-time Collaboration Tool (like Figma or Google Docs)

Key Challenges: Operational transformation (OT) vs. CRDTs, WebSocket scaling, and ensuring eventual consistency across thousands of concurrent users.

2. Design a Global Video Streaming Service (like Netflix/YouTube)

Key Challenges: CDN optimization, adaptive bitrate streaming (HLS/DASH), and handling massive "thundering herd" traffic during live events.

3. Design a Rate Limiter for a Public API

Key Challenges: Distributed counting (Redis/Memcached), sliding window vs. token bucket algorithms, and handling race conditions.

4. Design a Proximity Service (like Uber/Yelp)

Key Challenges: Quadtrees vs. Geohashing, efficient spatial indexing, and handling frequent location updates from drivers/users.

5. Design a Distributed Job Scheduler

Key Challenges: "At-least-once" vs. "exactly-once" delivery, leader election (Raft/Paxos), and handling worker failures.

How to Prepare

System design is open-ended. There is no single "correct" answer, but there are definitely wrong ones. The best way to prepare is to practice articulating your trade-offs.

Focus on Trade-offs: Don't just choose a database; explain why (e.g., "I chose Cassandra for its write throughput, accepting eventual consistency").
Back-of-the-envelope Math: Quickly estimate storage and bandwidth requirements.

Want to practice these scenarios? MockExperts' AI System Design Coach challenges you with these exact problems and grades your architectural decisions.