Design an online polling system
PremiumBackend systemMedium
- Real time
- Voting
- Scalability
Quick answer
This backend system interview question asks you to design an online polling system. Aim for a design that meets its requirements at the stated scale, then explain its main components, data flow and trade-offs. Interviewers want to see how you scope the problem, size it and defend each choice.
The problem
Design a real-time online polling system that supports poll creation, secure voting, and live result updates at scale.
What must an online polling system do?
- Users can create polls with questions, options, start time, and end time.
- Users can vote on active polls.
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How well must it do it?
- Vote submission should be low latency and highly available.
- The system should handle concurrent voting during traffic spikes.
4 more requirementsUnlock to see all
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Real time
- Voting
- Scalability
- Concurrency
- Rate limiting
- Live results
How you’ll practise
6 short steps · save and come back any time
- Requirements
- Estimate
- API and data
- High-level design
- Deep dives
- 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 backend system design round.
- Clarifies the requirements before drawing anything
- Uses a few numbers that actually change the design
- Draws a clear path from the client to storage
- Picks storage and caching with reasons, not by habit
- Explains what breaks first under load and how to fix it
- States trade-offs openly instead of claiming a perfect design
Questions people ask about this interview question
- Which design type is this question?
- It is a backend system question. You design an online polling system and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Medium. Entry-level engineers can practise it, but it expects you to reason about requirements and trade-offs, not only list components.
- What should I cover first?
- Start with the requirements: what the system must do, how well it must do it and which numbers change the design. 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