Design a live streaming platform like Twitch
PremiumReal-timeHard
- LL HLS
- Glass to glass latency
- Origin shield
Quick answer
This real-time interview question asks you to design a live streaming platform like Twitch. Aim for a design that delivers updates to many users with low delay, then explain connections, fan-out, ordering and trade-offs. Interviewers want to see how you keep latency low, handle reconnects and stay correct under load.
The problem
Design a live streaming platform like Twitch from the encoder onward: getting each stream to millions of viewers within a few seconds, live chat for huge channels, live viewer counts, go-live notifications and streamer drops. The hard part is a stream jumping from 2,000 to 2 million viewers without overloading the origin.
An encoder service already exists: it accepts each streamer's push and turns it into HLS and LL-HLS renditions. Your job starts where it ends.
What must a live streaming platform like Twitch do?
- Watch live: Viewers play a stream with under 5 seconds of glass-to-glass delay in normal mode; older players fall back to full 2-second segments with 10 to 15 seconds of delay.
- Live chat: Viewers send and read chat. A message appears for viewers with chat open within 2 seconds. A moderator can delete a message and it disappears for everyone.
How well must it do it?
- Origin protection: The origin serves each part a few dozen times at most, however many viewers watch.
- Spikes: A stream can go from 2,000 to 2 million viewers in a few minutes after a go-live push or a raid.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- LL HLS
- Glass to glass latency
- Origin shield
- Live chat
- Viewer counts
- Go live notifications
How you’ll practise
- Requirements
- Estimate
- Connections
- Message flow
- Delivery guarantees
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any real-time design round.
- Clarifies latency, ordering and delivery guarantees
- Chooses a connection model with reasons
- Explains fan-out to many receivers
- Handles reconnects, missed messages and duplicates
- Plans for hot spots and sudden traffic spikes
- States trade-offs between consistency and speed
Questions people ask about this interview question
- Which design type is this question?
- It is a real-time question. You design a live streaming platform like Twitch and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Hard. It suits engineers preparing for senior interviews, where you are expected to drive the discussion and go deep on trade-offs.
- What should I cover first?
- Start with who sends and receives updates, how fast they must arrive and what order matters. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team