With a rolling deployment, the server fleet is divided into a group, 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.