Rolling Update

Rolling Update is a deployment strategy that incrementally updates an application or system to a new version with minimal downtime. It works by replacing instances of the old version with instances of the new version one-by-one, rather than stopping the entire system at once.

During a Rolling Update, the system will have a mix of old and new versions running at the same time. The instances running the new version are brought up and tested before moving onto the next set of instances. If issues are detected, the deployment can be rolled back. This minimizes downtime and risk compared to stopping everything at once for an update.

For example, a Rolling Update could be used to deploy a new software version to a cluster of web servers. The update would start by deploying the new code to a few servers. After testing that these new servers work properly, the update would continue to roll out to more servers in batches. Traffic is shifted from old to new servers as the rollout progresses. The update completes when all old servers have been updated. If something goes wrong, the rollback happens one batch at a time.