Art of Codeartofcode
Lesson 1 of 15

43. Design Flash-Sale Ticket Booking (Ticketmaster / IRCTC Tatkal)

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The interview prompt
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43.1 What do you ask first?
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43.2 How big is this, really?
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43.3 What are the doors?
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43.4 What do we store?
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43.5 What does the whole system look like?
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43.6 How does the waiting room work?
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43.7 How does seat locking work?
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43.8 How do you rate-limit bots?
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43.9 How do you keep it fair?
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43.10 What would you say in the last five minutes?
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Score yourself
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Variations to practise
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Sources
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Code lab
43. Design Flash-Sale Ticket Booking (Ticketmaster / IRCTC Tatkal)

The interview prompt

3 min read+10 XP

This chapter is a full interview round, played out step by step. The interviewer's lines are in quotes. At each step you'll see what a strong candidate says, the pushback the interviewer throws, and how to answer it. At the end, grade yourself with the rubric.

How to use this chapter

  1. Read only the prompt below. Then stop.
  2. Set a 45-minute timer and do the whole round yourself, on paper or a whiteboard, out loud. Use the framework from Chapter 1: READ, then Draw, Dive, Defend.
  3. Then read the walkthrough and compare. Score yourself with the rubric at the end.

Flash sales break the usual rules: demand is far bigger than supply, it all arrives at the same second, and bots compete with people. Indian Railways' Tatkal tickets open a day before the journey, at 10:00 for AC classes and 11:00 for non-AC, and sell out in moments. When Ticketmaster opened the presale for Taylor Swift's Eras Tour in November 2022, it reported 3.5 billion system requests, about 4 times its previous peak, driven partly by bots.

The prompt

"Design the booking system for a massively popular event: tickets go on sale at 10:00, millions of people want them, and there are far fewer seats than buyers. It could be a stadium concert or Tatkal train tickets."

Stop here. Start your timer.