SYSTEM DESIGN BASICS - Save This!
Asked in Every Senior + Product Company Round!

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System Design is asked at Adobe, Microsoft,
Flipkart, Razorpay, Swiggy, Uber and ALL
product companies. Learn the basics NOW!

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1. SCALABILITY

Making your app handle more users over time

Vertical Scaling: Add more RAM/CPU to one server
-> Simple but has physical limits

Horizontal Scaling: Add more servers
-> Used by Google, Amazon, Netflix
-> Needs load balancer to distribute traffic

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2. LOAD BALANCER

Distributes incoming requests across servers
so no single server gets overloaded.

Algorithms:
Round Robin -> requests go in rotation
Least Connections -> send to least busy server
IP Hash -> same user always hits same server

Real examples: AWS ALB, Nginx, HAProxy

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3. CACHING

Store frequently accessed data in fast memory
to avoid hitting the database every time.

Redis -> most popular cache tool
CDN -> cache static files (images, CSS, JS)
near users geographically

Cache strategies:
Cache Aside -> app checks cache, then DB
Write Through -> write to cache + DB together
TTL (Time To Live) -> auto-expire cached data

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4. DATABASE DESIGN

SQL (MySQL, PostgreSQL):
-> Structured data, ACID transactions
-> Use for: banking, orders, user accounts

NoSQL (MongoDB, DynamoDB):
-> Flexible schema, high write speed
-> Use for: chat messages, logs, catalogs

Database Sharding:
-> Split data across multiple DB servers
-> Used when one DB cannot handle load

Replication:
-> Master writes, Slaves read
-> Improves read performance + availability

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5. MICROSERVICES vs MONOLITH

Monolith -> one big codebase, simple to start
Microservices -> split into small independent
services (User, Order, Payment, Notification)

When to use Microservices:
Large teams (each team owns one service)
Different scaling needs per service
Example: Netflix, Uber, Amazon all use it

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6. MESSAGE QUEUES

Async communication between services
so they don't have to wait for each other.

Tools: Apache Kafka, RabbitMQ, AWS SQS

Example: Order placed -> Queue -> Notification
service sends email without slowing checkout!

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7. CAP THEOREM

A distributed system can only guarantee 2 of 3:
C - Consistency (all nodes have same data)
A - Availability (always responds)
P - Partition Tolerance (survives network split)

Real systems choose CP or AP based on use case.

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TOP 5 SYSTEM DESIGN INTERVIEW QUESTIONS:

1. Design URL Shortener (like bit.ly)
2. Design Instagram (image storage + feed)
3. Design WhatsApp (real-time messaging)
4. Design Uber (ride matching + maps)
5. Design Netflix (video streaming + CDN)

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