System Design Concepts Basic

This is why i am making because of notes , if you are very beginner to learn system design , how the system in real time works . so let’s start this

What is a “System”?
Users → API → Logic → Data → Response

What is System Design ?
System Design is the process of designing a backend system that can handle real-world scale, failures, and growth.
System design is about deciding -

• How components talk to each other
• How data is stored, accessed, and scaled
• How the system behaves when things go wrong .

This process includes considerations such as scalability, performance, reliability, security, and cost efficiency, and it serves as the foundation for implementing and maintaining the system.
System design is not about writing code but about making high-level architectural decisions that balance trade-offs and ensure the system can handle expected loads, failures, and future growth.

System Design = Architecture + Data Flow + Trade-offs

Why System Design ?
Because single-machine thinking fails in real life
Let’s suppose
when app is one and small
then there is -> 1 server , 1 database and few users
But think what if user is so many in millions
then problem will occur like
Server crash , Database slow down , Deployments break down and Traffic becomes unpredictable
👉 System design exists to handle these problems BEFORE they happen.

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System Design is about preparing your system for success, failure, and growth — all at once.

Client–Server Model

Client–Server architecture is a system where:

• Client requests something (browser, app)
• Server processes the request and sends a response

The client doesn’t know how things work inside — it only cares about the result.

🌐 What Happens When You Open a Website?

1️⃣ You type a URL
2️⃣ DNS converts domain → IP address
3️⃣ TCP + HTTPS establish a secure connection
4️⃣ Request hits a load balancer / server
5️⃣ Backend logic runs
6️⃣ Data is fetched from cache / database
7️⃣ Response is sent back to the client

important question based on client server architecture :

1️⃣ Basics (Foundation)

1. What is client–server architecture?
2. Who is a client and who is a server?
3. Why don’t clients directly access databases?
4. What problems does client–server architecture solve?

2️⃣ Request Flow (End-to-End Thinking)

1. What happens when you type a URL in the browser?
2. Why do we check browser, OS, and router cache before DNS?
3. What is DNS and why is it needed?
4. Is DNS part of the backend system or external?
5. What happens if DNS fails?

3️⃣ Networking Layer

1. Why do we need TCP before HTTP?
2. What is the TCP 3-way handshake?
3. What happens if TCP connections are too many?
4. Why is TCP connection setup expensive at scale?

4️⃣ Security Layer (HTTPS / TLS)

1. Why is HTTPS mandatory today?
2. What happens during a TLS handshake?
3. Where does TLS usually terminate (backend or edge)?
4. What is the CPU cost of TLS and why does it matter?

5️⃣ Edge, CDN & Load Balancer

1. Why doesn’t the request go directly to backend servers?
2. What is an edge server?
3. What problems do CDNs solve?
4. What is a load balancer and why is it required?
5. What happens if one backend server goes down?

6️⃣ Backend Responsibilities (Core Focus)

1. What work actually happens in backend servers?
2. Why is caching critical in backend systems?
3. What is a cache hit vs cache miss?
4. Why is database access expensive?
5. What happens if the database becomes slow?

7️⃣ Performance & Failures

1. Where do most real-world delays happen?
2. Why is “slow internet” usually not the main problem?
3. What is latency vs throughput?
4. Why do backend engineers care about p95 / p99 latency?

8️⃣ Scalability Thinking

1. What breaks first when millions of users hit a system?
2. Why can’t we use one powerful server?
3. How does horizontal scaling help?
4. Which components scale easily and which don’t?

9️⃣ Reliability & Trade-offs

1. What happens when:

• a server crashes?
• cache fails?
• database is unavailable?

1. What trade-offs exist between

• performance vs cost
• consistency vs availability

We’ll definately know these all answers at the end of the day .