Rolling deployment

With a rolling deployment, the server fleet is divided into groups, so it doesn't need to be updated at the same time. The deployment process runs both old and new versions of software on the same server fleet but with different subgroups. A rolling deployment approach helps to achieve zero downtime as, if a new version deployment fails, then only a subgroup of servers is impacted from the entire fleet, and risk is minimal because half of the fleet will still be up and running. A rolling deployment helps to achieve zero downtime; however, deployment time is little more than in-place deployment.