Intro:
System design interviews are no longer reserved for senior engineers — even mid-level and entry-level devs are facing them in 2025.
The key to cracking them is knowing which questions appear again and again. Let’s look at the 7 most important ones.
🔹 1. Design a URL Shortener (Like bit.ly)
Concepts tested: Hashing, Database design, Scalability.
Interview tip: Always mention collision handling.
🔹 2. Design a Cache System (Like Redis)
Concepts: Caching strategies (LRU, LFU), Expiry, Consistency.
Interview tip: Mention trade-offs between speed and memory.
🔹 3. Design a Load Balancer
Concepts: Round robin vs weighted, Failover, Health checks.
Interview tip: Always show a diagram.
🔹 4. Design a Chat Application (Like WhatsApp)
Concepts: WebSockets, Message queues, Storage models.
Interview tip: Don’t forget real-time delivery guarantees.
🔹 5. Design a Rate Limiter
Concepts: Token bucket, Leaky bucket, Fixed window counters.
Interview tip: Explain why rate limiting is critical for APIs.
🔹 6. Design YouTube (Video Streaming System)
Concepts: CDN, Sharding, Metadata management, Thumbnails.
Interview tip: Stress on high availability.
🔹 7. Design an E-commerce System (Like Amazon)
Concepts: Inventory management, Payment flows, Recommendations.
Interview tip: Talk about microservices and scalability.
✅ Final Thoughts
In 2025, these 7 problems cover 80% of what system design interviews actually ask.
Don’t just memorize answers — focus on trade-offs (scalability vs cost, speed vs consistency).
👉 Call to Action:
I’ve created detailed step-by-step diagrams, flowcharts, and interview notes for these questions here:
FullStackPrep.dev – System Design Interview Prep
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