0. How to Deliver Answer

---

1️⃣ Types of Questions

• Product Design
  • Apps like Uber, Netflix, Dropbox
• Infrastructure Design
  • Rate limiter
  • Message queue
  • Data pipeline

---

2️⃣ Standard Interview Framework

Step-by-step R → E → A → D → D

step-by-step.excalidraw

1. Requirements (~5 min)

Functional Requirements

• Defines

  • what the system does == define the features of the system
  • Format: Users should be able to...

• Example (Twitter):

  • Post tweets
  • Follow users
  • View feed

• Tips:
  • Focus on top 3 features only

---

Non-functional Requirements

• how the system should behaves

• Examples:

  • High availability
  • Low latency (<200ms)
  • Scale (100M+ users)

• FR Vs NFR

  • FR: User can upload photo
  • NFR: Photo upload should finish within 2 sec

---

2. Core Entities (~2 min)

• Example: Define main data objects
  • User
  • Tweet
  • Follow

• How to identify:

  • Who are actors?
  • What are main resources?

• Tips:

  • Start small → expand later
  • Avoid over-designing schema early
    • i am not gonna details the key filed and column yet i don't quite know that yet. i am too early in my design. they are gonna evolve naturally. As when i move to high level design I will be explicit about exactly the filed that matter So, For now i would stop here.

---

3. APIs (~5 min)

Look for the FR. then try to satisfy that with API REST API ✅
POST /tweets
GET /tweets/{id}
POST /follows
GET /feed

---

4. High-Level Design

• Goal: Build working system first

• Approach:

  • Draw servers
  • Draw database
  • Draw cache
  • Draw load balancer
  • Map APIs → system flow
  • Just Create Request → Server → DB → Response then enhance later

• *Key Tips:

  • Start simple ✅
  • Add complexity later ⚠️
  • Explain data flow clearly
  • Show:
    • Where data is stored
    • What changes per request

• Common Mistake:*

  • Adding cache, queues, sharding too early ❌

---

5. Deep Dive (~10 min)

• *Goal: Improve system for:

  • Scale
  • Performance
  • Reliability
  • You can deep dive to few places in high level design

• *What to do:

  • Handle bottlenecks
  • Handle edge cases
  • Add:
    • Caching
    • Sharding
    • Load balancing

• *Example (Twitter Feed):

  • Fanout-on-read vs fanout-on-write
  • Use cache for faster reads

• *Pro Tips:

  • Junior → let interviewer guide
  • Don’t dominate conversation
  • Give interviewer space to probe

---

3️⃣ TIPS

1. Use ONE simple mnemonic

SCALE

• S → Scalability
• C → CAP
• A → Availability / Fault tolerance
• L → Latency
• E → Environment - mobile / web

👉 Enough for interviews ✅

---

2. Learn to CONTROL the interview (soft skill)

If interviewer interrupts:

Say:

“I can dive deeper here, but I’d like to first complete the high-level design and then come back”

---

3. Don’t memorize answers, learn thinking

❌ Wrong mindset:

• “Should I use Kafka?”

✅ Right mindset:

• “Do I need async processing?”

---

4. Always mention trade-offs

Example:

“I’ll use cache to reduce latency, but this introduces consistency challenges”

👉 This is what interviewers LOVE

---

5. Add 1–2 advanced points (edge boost 🚀)

From comments:

• Monitoring & metrics
• Bottleneck detection
• Query patterns

👉 Just mentioning these = strong signal

---

6. Final Recommendation

Your compact interview mental model should be:

1. Clarify top 3 functional requirements  
2. Clarify top 3 NFRs  
3. List core entities  
4. Define API/interface  
5. Draw simple end-to-end design  
6. Deep dive into bottleneck  
7. Add scaling + reliability + monitoring

And remember this

Do not fight the interviewer’s flow.  
Stay structured even when interrupted.

---