Feature Flag Service — Notes

Functional

• Boolean / multi-variate flags.
• Targeting rules (user, attribute, segment).
• Percentage rollout, sticky.
• Kill switch, scheduled rollouts.
• Per-environment.

Non-functional

• Evaluation latency < 1 ms with local SDK.
• Push propagation < 10 s.
• Highly available reads even on control plane outage (stale cache OK).

Trade-offs

• Local evaluation vs server evaluation: local is fast; server centralizes audit.
• GitOps vs UI flags: GitOps for release flags, UI for ops kill switches.

Refs

• LaunchDarkly architecture, GrowthBook, Unleash, Flipt.
• "Feature flags considered harmful" critiques.