Q: How would you design a ticket booking system like Ticketmaster?

**Target Audience:** Backend engineers preparing for the "design Ticketmaster" round, which is really a question about contention, holds and admission control. **Difficulty:** Hard **Verified with:** Node 22.22 and Python 3.12 (identical output). The Eras Tour figures are from Ticketmaster's statement of November 2022 as reported by CBS News and Cox Media Group stations. > **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you als

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

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 3

When would you use WebSockets vs polling vs SSE?

Accepted Answer

**Target Audience:** Beginners to system design who have built a web page that calls an API; no networking background assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Protocol facts are cited from RFC 6455, RFC 8441, MDN and the AWS load balancer docs.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the words an interviewer expects. Numbers come from r

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 does caching work end-to-end (where, what, when) — cache-aside vs write-through?

Accepted Answer

# How Does Caching Work End-to-End? Where, What, and When (Cache-Aside vs. Write-Through) **Target Audience:** Junior & Senior Software Engineers preparing for System Design Interviews — assumes basic familiarity with the idea of a cache. **Difficulty:** Medium > This doc builds on the Caching guide (eviction policies, LRU) and the

Question 6

How does caching improve system performance?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a database query is; no caching 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, latencies and counts come from running the example; the **Verified** section quotes the full outpu

Question 7

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

Accepted Answer

## Step 1: Use Cases, Constraints, Assumptions, Back-of-Envelope

### Use cases
We'll scope to handle only the core flows that expose the bottlenecks; everything else is deferred.

- **User** creates a paste / short URL — POST long URL or text, get back `https://sho.rt/Ab3x9K` (302 redirect for URL, render for paste).
- **User** reads a paste/short URL — GET `/Ab3x9K`, cache-hit serves in <10ms, miss hits DB then populates cache.
- **Service** generates short code — deterministic Base62 of auto-

Question 8

How would you design a ticket booking system like Ticketmaster?

Accepted Answer

**Target Audience:** Backend engineers preparing for the "design Ticketmaster" round, which is really a question about contention, holds and admission control.
**Difficulty:** Hard
**Verified with:** Node 22.22 and Python 3.12 (identical output). The Eras Tour figures are from Ticketmaster's statement of November 2022 as reported by CBS News and Cox Media Group stations.

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

Question 9

Advanced feature flags — targeting, gradual rollout, and edge evaluation?

Accepted Answer

**Target Audience:** Intermediate engineers who know what a feature flag is (see the [feature flag system design](/interview-question/how-would-you-design-a-feature-flag-system-launchdarkly-style-at-scale)) and want the evaluation internals; every term is still defined.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 for the bucketing example (identical output); Node and Python for the edge example. LaunchDarkly bucketing facts are from the LaunchDarkly perce

Question 10

How would you design a URL shortener like TinyURL?

Accepted Answer

**Target Audience:** Engineers who know the basic shortener design (codes, a table keyed by code) and want to go deep on scaling reads; caching terms are defined as they come up.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). HTTP caching rules for redirects checked against RFC 9110 in October 2026.

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

SYSTEM DESIGNDECODED.

Easy

How does DNS resolution work?

Medium

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

When would you use WebSockets vs polling vs SSE?

What is a CDN and how does it work?

How does caching work end-to-end (where, what, when) — cache-aside vs write-through?

How does caching improve system performance?

Hard

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

How would you design a ticket booking system like Ticketmaster?

Advanced feature flags — targeting, gradual rollout, and edge evaluation?

How would you design a URL shortener like TinyURL?

How would you design Instagram?

How would you design a system that scales to millions of users on AWS?

How would you design YouTube?

How would you design Google Maps?