βΆFeature flagging vs feature flags β what's the difference?
Feature flags are the toggle mechanism (boolean on/off, percentage rollouts). Feature flagging is the system design discipline: how you architect rollout strategy, manage flag lifecycle, integrate with experiments, prevent technical debt, and scale flag management across teams. Think flags (tool) vs flagging (practice). This skill covers the architecture, process, and strategic layer.
βΆWhat's the relationship between feature flagging and trunk-based development?
Trunk-based development = all engineers commit to main/trunk daily, never long-lived branches. Feature flagging enables this: you ship incomplete features on trunk (behind flags), deploy multiple times daily, and progressively roll out. Without flags, trunk-based dev would expose broken code to users. Flags are the safety net.
βΆHow do I avoid flag technical debt?
Set a kill-date when you create a flag (e.g. 'remove by 2026-05-15'). Track flag lifecycle: creation, ramp (1% β 10% β 100%), deprecation. Audit flags weekly in CI. Automatically fail tests if old flags (>90 days) are still in code. Archive flags properly β don't just delete. Most teams accumulate 200+ dead flags; the cost is real: slower tests, cognitive load, higher bugs.
βΆHow do multivariate flags differ from A/B testing flags?
A/B testing flags (2 variants: control vs treatment) measure statistical significance. Multivariate flags (3+ variants: A/B/C/D) explore parameter space. Multivariate needs larger sample size. Use A/B for shipping decisions (ship or kill). Use multivariate for optimization (which variant wins). Most platforms support both; the difference is statistical rigor and sample size planning.
βΆWhat's the OpenFeature standard and why does it matter in 2026?
OpenFeature (CNCF 2024) is a vendor-neutral specification for flag evaluation: one SDK interface (open-feature-sdk) that swaps providers (LaunchDarkly β Statsig β PostHog). Reduces lock-in. In 2026, major platforms (Statsig, Eppo, GrowthBook) support it. Start with OpenFeature if you're unsure which provider long-term.
βΆHow do I measure flag impact on system performance (latency, cold starts)?
Flag evaluation is synchronous and must be <10ms p99. Use local flag caches (SDK caches rules in-process) rather than remote calls per request. Measure flag evaluation time in observability stack (CloudWatch, Datadog, New Relic). Monitor for 'flag thrashing' (flags changing during user session). For global flags, consider edge caching (Cloudflare, Vercel Edge). For critical paths, pre-compute flag state on service init.
βΆWhat's a realistic cost for a feature flagging platform in 2026?
Unleash (open-source, self-hosted): free but ops overhead. LaunchDarkly: $200-500/month (small team), $2k+/month (enterprise). Statsig, Optimizely, Eppo: $500-3k/month depending on event volume and team size. PostHog (flags + analytics): $450+/month all-in. Flagsmith, Split.io: $200-1k/month. Most bootstrap with Unleash or PostHog, migrate to LaunchDarkly when scale justifies the cost.