Question 1

How does DNS resolution work?

Accepted Answer

**Target Audience:** Beginners to system design — you have used a browser; no networking background assumed.
**Difficulty:** Easy
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Behaviour claims come from running the example; the **Verified** section quotes the full output.

## 1. Why This Even M

Question 2

What is the difference between a reverse proxy and a forward proxy?

Accepted Answer

**Target Audience:** Beginners to system design — you know a browser talks to a server; no networking background assumed.
**Difficulty:** Easy
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Behaviour shown comes from running the example; the **Verified** section quotes the full output.

## 1. Wh

Question 3

What latency numbers and availability targets should every engineer know?

Accepted Answer

**Target Audience:** Beginners — no hardware or operations background assumed.
**Difficulty:** Easy
**Verified with:** Node 22.22 and Python 3.12 (the calculator prints the same output in both).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every derived number was computed by the example program; the **Verified** section quotes its full output.

## 1. Why This Even Mat

Question 4

How do you design for high availability?

Accepted Answer

**Target Audience:** Beginners to reliability engineering — you know what a server, a load balancer and a database are; every reliability term is defined as we go.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). All component availabilities in the run are stated assumptions, not vendor SLAs; AWS health-check defaults are from the Amazon Route 53 Developer Guide, checked in October 2026.

> **How to read this doc:** Every idea is explained in pl

Question 5

Edge caching on Cloudflare — how do you get 95%+ hit rate without stale data?

Accepted Answer

**Target Audience:** Intermediate — you know what a CDN does; Cloudflare-specific settings and terms are explained here.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Cloudflare product behaviour is taken from Cloudflare documentation and changelog entries cited inline, checked in October 2026.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words

Question 6

What is the difference between REST and GraphQL?

Accepted Answer

**Target Audience:** Beginners to system design — you have called an HTTP API; no GraphQL experience assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Request counts and byte sizes come from running the example; the **Verified** section quotes the full output.

## 1.

Question 7

What is the CAP theorem and how does it drive consistency vs availability tradeoffs?

Accepted Answer

# CAP Theorem: Consistency vs. Availability Tradeoffs (Beginner-Friendly Guide)

**Target Audience:** Junior & Senior Software Engineers preparing for System Design Interviews — no prior system design knowledge assumed.
**Difficulty:** Easy to Medium

> **How to read this doc:** Every concept is explained in plain language first. Right after, you'll see a callout like `📌 Interview term:` — that's the exact vocabulary a senior engineer would use for the same idea.

## 1. Why This Even Matters —

Question 8

When would you choose SQL vs NoSQL?

Accepted Answer

**Target Audience:** Beginners to system design — you have used a spreadsheet or a database table; no database internals assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Behaviour shown comes from running the example; the **Verified** section quotes the full output.

Question 9

What is the difference between horizontal and vertical scaling?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a server and a database are, nothing more.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (the example prints the same table in both).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every number below comes from actually running the example program; the **Verified** section quotes its f

Question 10

What is idempotency and why does it matter?

Accepted Answer

**Target Audience:** Beginners who have built or called a web API and want to understand why retries are dangerous and how real systems make them safe.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). HTTP method semantics are cited from RFC 9110; Stripe behaviour from the Stripe API reference ("Idempotent requests"); the Idempotency-Key header from the IETF httpapi working-group Internet-Draft.

> **How to read this doc:** Every idea is explain

SYSTEM DESIGNDECODED.

Easy

How does DNS resolution work?

What is the difference between a reverse proxy and a forward proxy?

What latency numbers and availability targets should every engineer know?

Medium

How do you design for high availability?

Edge caching on Cloudflare — how do you get 95%+ hit rate without stale data?

What is the difference between REST and GraphQL?

What is the CAP theorem and how does it drive consistency vs availability tradeoffs?

When would you choose SQL vs NoSQL?

What is the difference between horizontal and vertical scaling?

What is idempotency and why does it matter?

How do you handle asynchronism, message queues and backpressure at scale?

Hard

How would you design a distributed job scheduler?

How would you design a URL shortener like TinyURL? (Pastebin / Bit.ly)

How would you design a ticket booking system like Ticketmaster?

What is leader election in distributed systems?

How would you design a news feed system?

How would you design a distributed cache?

How would you design a notification system?

How do you make a payment system reliable against retries?