When you set up or import a vSphere Lifecycle Manager image to use with a cluster, the software specified in the image is not immediately installed on the hosts in that cluster. To apply the software specification from the image to the hosts, you must remediate the cluster against that image.
To initiate remediation of a cluster, you must have the required privileges. For a list of all vSphere Lifecycle Manager privileges and their descriptions, see vSphere Lifecycle Manager Privileges For Using Images. For more information about managing users, groups, roles, and permissions, see the vSphere Security documentation.
In vSphere 7.0, the hosts in a cluster are remediated sequentially. Parallel remediation is not supported. So, if the remediation for a single host in the cluster fails, the remediation of the entire cluster stops.
During remediation, the image that you set up for the cluster is installed on all ESXi hosts in the cluster.
When you remediate a cluster that contains a single ESXi host or that has vSphere Storage DRS disabled or in manual mode, the remediation process cannot put that host into maintenance mode. So, to proceed with the remediation, you must power off the virtual machines that are running on the host, move them to another host, or select a user policy that allows the remediation process to power off the virtual machines. You can also set a user policy to power on the virtual machines after the host is remediated.
For vSAN clusters, the remediation operation includes a hardware compatibility check. Depending on how you configure the vSphere Lifecycle Manager remediation settings, vSphere Lifecycle Manager might not proceed with the remediation task if hardware compatibility issues exist. For information about configuring the global vSphere Lifecycle Manager remediation settings, see Configure Remediation Settings for vSphere Lifecycle Manager Images. For information about configuring the remediation settings for a particular cluster, see Edit the Remediation Settings for a Cluster.
If the update requires, hosts are put into maintenance mode before remediation. Virtual machines cannot run when a host is in maintenance mode. To ensure a consistent user experience,vCenter Server migrates the virtual machines to other hosts within the cluster before a host is put into maintenance mode. vCenter Server can migrate the virtual machines if the cluster is configured for vMotion and if DRS and VMware Enhanced vMotion Compatibility (EVC) are enabled. EVC guarantees that the CPUs of the hosts are compatible, but it is not a prerequisite for vMotion.