Store configuration in the environment, not in the code. Validate configs in CI before deployment. If staging and production drift apart, you are testing assumptions, not reality.
Strong answers cover: externalised configuration (not baked into images), environment-specific config files or services, config validation in CI, drift detection, and maintaining environment parity to reduce "works on staging but not production" issues. Best candidates discuss twelve-factor app principles and immutable infrastructure approaches.
Core operational skill. Configuration issues cause a disproportionate number of production incidents. Candidates who have systematic configuration management prevent an entire category of outages.