> There are [important changes to the upgrade process](/ee/upgrade) that, if not correctly followed, can have impact on the availability of applications running on the Swarm during upgrades. These constraints impact any upgrades coming from any version before `18.09` to version `18.09` or greater. See [Cluster Upgrade Best Practices](/ee/upgrade.md#cluster-upgrade-best-practices) for more details. Additionally, to ensure high availability during the DTR upgrade, you can also drain the DTR replicas and move their workloads to updated workers. To do this, you can join new workers as DTR replicas to your existing cluster and then remove the old replicas. See [docker/dtr join](/reference/dtr/2.6/cli/join) and [docker/dtr remove](/reference/dtr/2.6/cli/remove) for command options and details.
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