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rb-011

Incident after a feature flag change

CheckoutErrorRateHighwebcheckoutpayments

Signs a flag is the cause

  • A flag changed shortly before the errors began.
  • The errors affect only some users, and error logs list the flag in their flags field (checkout records which flags were active for the request).
  • The error rate tracks the flag's rollout percentage.

Mitigation

Switch the flag off. Flags apply within seconds without a deploy, and switching off is always reversible. Tell the flag owner (the person in the flag change event).