System Design Framework

A structured approach to tackle any system design interview

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45-60 Minute Interview Timeline

Requirements Clarification(5-7 minutes)
→
Back-of-Envelope Calculations(3-5 minutes)
→
High-Level Design(10-15 minutes)
→
Deep Dive(15-20 minutes)
→
Bottlenecks & Trade-offs(5-10 minutes)
01

Requirements Clarification

5-7 minutes

Ask questions to understand the scope, constraints, and requirements

Key Questions to Ask/Consider:

  • What are the main features we need to support?
  • What is the expected scale (users, requests, data)?
  • What are the latency requirements?
  • Should we focus on any specific aspect of the system?
  • What are the non-functional requirements (availability, consistency)?
  • Are there any specific constraints (budget, timeline, technology)?

💡 Senior Engineer Tips

  • • Push back on ambiguous requirements - senior engineers know what details matter
  • • Consider regulatory and compliance requirements upfront
  • • Ask about existing systems and migration constraints
  • • Discuss SLA requirements explicitly
02

Back-of-Envelope Calculations

3-5 minutes

Estimate scale to inform design decisions

Key Questions to Ask/Consider:

  • Daily/Monthly Active Users (DAU/MAU)
  • Requests per second (read/write ratio)
  • Data storage requirements
  • Bandwidth requirements
  • Peak vs average load

Quick Calculations:

QPS:DAU × actions/day ÷ 86,400 seconds
Storage:Objects × size × retention × replication
Bandwidth:QPS × average response size

💡 Senior Engineer Tips

  • • Use powers of 2 for quick mental math
  • • Consider growth trajectory, not just current numbers
  • • Factor in replication and backup overhead
  • • Mention regional distribution impact on calculations
03

High-Level Design

10-15 minutes

Draw the main components and their interactions

Key Questions to Ask/Consider:

  • What are the main components needed?
  • How do clients interact with the system?
  • What are the data flows for main use cases?
  • Where do we need caching?
  • How do we handle reads vs writes?

Common Components:

Load Balancer / API GatewayApplication ServersDatabase (SQL/NoSQL)Cache LayerMessage QueueCDNExternal Services

💡 Senior Engineer Tips

  • • Start with the simplest design that could work
  • • Use standard architectural patterns (don't reinvent)
  • • Consider multi-region from the start
  • • Identify single points of failure early
04

Deep Dive

15-20 minutes

Drill into critical components based on interviewer guidance

Deep Dive Areas:

Data Model
  • • Schema design
  • • Indexing strategy
  • • Partitioning/Sharding
  • • Denormalization decisions
API Design
  • • Endpoints
  • • Request/Response formats
  • • Authentication
  • • Rate limiting
  • • Versioning
Algorithm/Logic
  • • Core business logic
  • • Matching/Ranking algorithms
  • • Consistency guarantees
Scaling
  • • Horizontal scaling points
  • • Caching strategy
  • • Database scaling
  • • Async processing

💡 Senior Engineer Tips

  • • Discuss trade-offs explicitly for every decision
  • • Mention operational concerns (monitoring, debugging)
  • • Consider failure modes and recovery strategies
  • • Reference real-world implementations when relevant
05

Bottlenecks & Trade-offs

5-10 minutes

Identify issues and discuss solutions

Common Issues & Solutions:

⚠️ Single Points of Failure
✓ Replication✓ Failover✓ Multi-region
⚠️ Scalability Bottlenecks
✓ Sharding✓ Read replicas✓ Caching✓ CDN
⚠️ Consistency vs Availability
✓ CAP trade-offs✓ Eventual consistency✓ Conflict resolution
⚠️ Cost Optimization
✓ Tiered storage✓ Auto-scaling✓ Reserved capacity

💡 Senior Engineer Tips

  • • Proactively identify issues before being asked
  • • Quantify impact of bottlenecks
  • • Propose incremental improvements with milestones
  • • Consider operational cost, not just infrastructure

❌ Common Mistakes to Avoid

✗ Diving into details too early

✓ Start with requirements and high-level design first

✗ Not asking clarifying questions

✓ Spend first 5-7 minutes understanding the problem

✗ Over-engineering the solution

✓ Start simple, then add complexity as needed

✗ Ignoring non-functional requirements

✓ Explicitly discuss scalability, availability, consistency

✗ Not discussing trade-offs

✓ Every decision has pros/cons - articulate them

✗ Monologue without interaction

✓ Check in with interviewer, ask for feedback

✗ Giving up when stuck

✓ Think out loud, ask for hints, reason from first principles

✗ Not leveraging experience

✓ Reference relevant past projects and learnings

🎤 Senior Engineering Key Phrases

"Let me clarify the requirements first..."
"Given the scale, we should consider..."
"The trade-off here is..."
"Based on the read/write ratio..."
"For consistency requirements, I'd choose..."
"One potential bottleneck is..."
"To handle failures, we could..."
"Let me walk you through the data flow..."

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