A kill switch is a feature flag designed for incident response. When a feature causes errors, latency, data risk, or support volume, the kill switch turns the risky behavior off while the application keeps running.
The best kill switches are boring. Everyone knows where they are, what they disable, and what safe behavior remains after they are turned off.
Design the safe path first
A kill switch is only useful if `false` is a known safe path. The fallback might be the old checkout, a simpler scoring model, a cached response, or a disabled optional workflow.
Name flags by behavior
- Use `new-checkout-flow` instead of `temporary-fix`.
- Use `billing-retry-worker` instead of `flag-123`.
- Document who owns the flag and when it should be removed.
Test the off path
Do not wait for an incident to discover that the off path has drifted. Run the disabled path in staging, create a small production cohort, and verify the fallback before expanding the rollout.
Audit every emergency change
A kill switch often changes user-visible behavior quickly. Audit logs help teams understand who changed it, why support tickets changed, and when it is safe to re-enable the feature.
Related docs
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