What is a Rolling Update?
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Quick Answer
A rolling update gradually replaces old instances with new ones a few at a time, keeping the service available throughout, with no separate second environment.
Detailed Answer
It is the default Kubernetes Deployment strategy, controlled by maxSurge and maxUnavailable, and gated by readiness probes so traffic only flows to healthy new pods. Rollback re-runs the process with the previous version. It is cheaper than blue-green but the two versions coexist briefly, so changes must be backward compatible.
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Interview Tip
Note maxSurge/maxUnavailable and readiness probes, and that both versions run at once so changes must be backward compatible.
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