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.

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Question 2

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 3

What is a load balancer and what strategies does it use?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a web server is; no networking background assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four 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. All numbers come from actually running the example; the **Verified** section quotes the f

Question 4

What is a CDN and how does it work?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a web server is; no networking background 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. Hit ratios and fetch counts come from running the example; the **Verified** section quotes the full output.

##

Question 5

How would you design a Web Crawler?

Accepted Answer

**Target Audience:** Engineers preparing for a system design round; no prior knowledge of crawling or search engines is assumed, and every term is defined when it first appears.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). The robots.txt standard (RFC 9309) and search engine handling of `Crawl-delay` checked against the RFC and Google Search Central in October 2026.

> **How to read this doc:** Every idea is explained in plain language first,

SYSTEM DESIGNDECODED.

Easy

How does DNS resolution work?

Medium

How do you design for high availability?

What is a load balancer and what strategies does it use?

What is a CDN and how does it work?

Hard

How would you design a Web Crawler?