Design a simple feature flag system
PremiumBackend systemEasy
- Beginner
- System design
- Configuration
Quick answer
This backend system interview question asks you to design a simple feature flag 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 feature flag system that allows teams to control feature availability dynamically for users, groups, environments, or rollout percentages.
What must a simple feature flag system do?
- Developers can create, update, enable, and disable feature flags.
- Flags can be applied globally or to specific users or groups.
5 more requirementsUnlock to see all
How well must it do it?
- Flag evaluation should be low latency.
- The system should remain available even if the central flag service is temporarily down.
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
- Beginner
- System design
- Configuration
- Ab testing
- Feature flags
- User targeting
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 a simple feature flag system and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Easy, so it suits engineers who are new to backend system interviews. It is also a good warm-up before harder questions.
- 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.
Related questions
Updated · Written by the SevyDevy team