rollback

The interviewer does not want the three definitions. They want a decision, the number that justifies it, and what you do when the canary looks fine for nine minutes and then does not.

The deployment question that has a real answer and a real trap. Code and schema deploy at different speeds, and any step where they must change together is the step that causes the outage.

Redeploying the old tag reverses code and nothing else. What separates staff-level answers is a per-change map of what rolls back in seconds, what rolls back in days, and what only moves forward.

The code did not change, the data did. That inverts what triggers the pipeline, what the tests assert, and what a rollback means.

Drawing an agent that polls a server is the easy third. The interview is about partial applies, fleet-versus-world state, and why rollback must be a pointer flip, never a reverse edit.