System design interview question
"Design Discord. Servers contain channels; a channel can have 500,000 members, and when something happens in a game, tens of thousands of them are typing at once. Plus persistent voice channels. 150 million monthly users, 4 billion messages a day."
massive-fan-out real-time broadcast — the extreme end of the messaging spectrum. WhatsApp caps groups at 1,024; Slack channels are mostly small. Discord's defining case is a single channel with 500,000 concurrent listeners, which forces a subscription/topic model rather than per-recipient fan-out. Voice adds a second, genuinely different media plane.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
Book a free mock interviewAll 132 system design interview questions
System design mock interviews · DSA interview questions · Free mock interview practice · Browse interviewers · Sign in