Feature flags + A/B testing basics
Comes up in: Frontend system design, Hiring manager
This concept is being written. It gets the full five steps — explanation, predict, interview angle, practice with tests, and review cards. Here is exactly what it will cover, so you can study it elsewhere in the meantime.
What it covers
- release vs ops vs permission vs experiment flags
- client vs server evaluation
- avoiding flicker
- flag debt and cleanup
- kill switches
- hypotheses
- randomisation and sticky assignment
- sample size and significance (intro)
- guardrail metrics
- peeking problem
Words you will know
What you will practise
- add a flag with gradual rollout
- design an experiment for a new checkout button
Interview questions this answers
- How would you implement feature flags in a frontend without UI flicker?
- How do you prevent feature flags from becoming tech debt?
- How would you run an A/B test on a pricing page?