"Design TikTok's video processing pipeline." This was the system design question that made me freeze during my first senior developer interview. Today, after architecting systems at scale and conducting hundreds of technical interviews, I know exactly what companies are looking for - and it's not just throwing around buzzwords like "microservices" and "Kubernetes."

Here's the truth: most developers approach system design interviews wrong. They jump straight into solutions without understanding the real requirements. After helping thousands of developers through QuizMaster's system design track, I've developed a framework that consistently leads to success.

The ROADS Framework for System Design Success

Before diving into specific questions, let's establish the framework that's helped our students land senior roles at top tech companies:

• Requirements clarification: Understand the scale and constraints
• Outline high-level design: Start with the big picture
• API design: Define clear interfaces
• Data model: Choose the right storage solutions
• Scale considerations: Address bottlenecks

1. Understanding Scale: The Numbers Game

One mistake I see constantly: candidates don't ask about numbers. Here's what you should always clarify:

Key Metrics to Discuss:
- Daily Active Users (DAU)
- Read vs Write ratio
- Data storage requirements
- Bandwidth considerations
- Latency requirements

🔥 Pro Tip: Frame these questions in business terms. Instead of asking "What's the QPS?", ask "How many users are we expecting to serve simultaneously?"

2. Real-World Example: Designing Instagram's Feed

Let's apply this to a real interview question I frequently ask candidates:

Step 1: Requirements Gathering

Bad approach: "I'll use a microservices architecture with Redis caching." Good approach: Let's understand the requirements first:

Functional Requirements:
- Post photos and videos
- View feed
- Like and comment
- Follow users

Non-Functional Requirements:
- Low latency for feed loading (<500ms)
- High availability (99.99%)
- Eventually consistent model acceptable
- Global access

Step 2: Data Model Design

Here's a schema design that impressed my interviewer at Meta:

-- User profile storage
CREATE TABLE users (
    user_id UUID PRIMARY KEY,
    username VARCHAR(50) UNIQUE,
    email VARCHAR(255),
    created_at TIMESTAMP
);

-- Content metadata
CREATE TABLE posts (
    post_id UUID PRIMARY KEY,
    user_id UUID REFERENCES users(user_id),
    media_url VARCHAR(255),
    caption TEXT,
    created_at TIMESTAMP,
    location_data JSONB
);

-- Relationships
CREATE TABLE follows (
    follower_id UUID REFERENCES users(user_id),
    followee_id UUID REFERENCES users(user_id),
    created_at TIMESTAMP,
    PRIMARY KEY (follower_id, followee_id)
);

3. The Scalability Toolkit

Here are the patterns that repeatedly come up in interviews:

Load Balancing Strategy

Client → CDN → Load Balancer → Application Servers
                            ↳ Cache Layer
                            ↳ Database Cluster

💡 Key Insight: "In my experience, candidates often overlook global load balancing. When I'm interviewing at companies like Google, I always discuss multi-region deployment strategies."

Caching Strategy

Think in layers:

1. Browser Cache (client-side)
2. CDN (edge caching)
3. Application Cache (Redis/Memcached)
4. Database Cache

4. Real Interview Questions & Solutions

Here are three questions I frequently ask when interviewing senior developers:

Question 1: Design a URL Shortener

Key considerations:

• Hash function selection
• Collision handling
• Analytics requirements

Question 2: Design Twitter's Trending Topics

Critical components:

• Stream processing
• Temporal aggregation
• Regional trending

Question 3: Design a Distributed Task Scheduler

Important aspects:

• Task persistence
• Failure handling
• Leader election

5. Common Pitfalls to Avoid

From conducting over 200 system design interviews, here are the top mistakes I see:

1. Not Clarifying Requirements

   • Bad: Jumping straight into technology choices
   • Good: "Let me understand the scale we're targeting..."

2. Ignoring Trade-offs

   • Bad: "We'll use Cassandra for everything"
   • Good: "For user profiles, we'll use PostgreSQL for ACID compliance, but for events, we'll use Cassandra for high write throughput..."

3. Skipping Monitoring

   • Bad: "The system will handle failures automatically"
   • Good: "We'll need monitoring for these key metrics..."

Ready to Master System Design?

We've covered the fundamental patterns for system design interviews. Want to practice with real scenarios? QuizMaster's System Design track offers:

• Interactive design sessions
• Real-time feedback
• Industry expert reviews
• Performance analytics

Start Your Design Journey →

Remember: Great system design skills aren't built overnight. They come from understanding patterns, practicing real scenarios, and learning from experienced architects.

See you in the design review! 🚀

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