When you manage а vSAN stretched cluster or a two-node ROBO cluster with a single image, vSphere Lifecycle Manager can manage both the hosts in the cluster and the dedicated witness host. That is, you can check the compliance status of the witness host and remediate it against the cluster image.

What Is a Stretched Cluster?

A stretched cluster is a deployment model in which two or more hosts are part of the same logical cluster but are located in separate geographical locations. Every vSAN stretched cluster or two-node ROBO cluster has a witness host, which is a standalone host that is not a member of the respective cluster but is associated with it. The witness host of a vSAN cluster is managed by the same vCenter Server where the respective stretched or ROBO cluster resides.

vSphere Lifecycle Manager and the vSAN Witness Hosts

The vSAN witness host is a physical or virtual ESXi host that contains the witness components of virtual machine objects stored in the vSAN cluster. The witness host does not support workloads and is not a data node. A single stretched or two-node ROBO cluster can have only one witness host.

In earlier vSphere releases, you can use a single vSphere Lifecycle Manager image to manage the hosts in a vSAN stretched cluster or a two-node ROBO cluster, but the only way to manage the witness host is through vSphere Lifecycle Manager baselines. Starting with vSphere 7.0 Update 3, you can use vSphere Lifecycle Manager images to manage a vSAN stretched cluster and its witness host. The following requirements exist:
  • vCenter Server must be version 7.0 Update 3 and later.
  • The witness host must be ESXi version 7.0 Update 2 and later.
  • The witness host must be a virtual server and not a physical server.
  • The witness host must be a dedicated witness host and not a shared witness host.
You start using vSphere Lifecycle Manager images to manage the witness host by performing any of the following tasks:
  • You switch from using vSphere Lifecycle Manager baselines to using vSphere Lifecycle Manager images for an existing vSAN stretched or two-node ROBO cluster.
    Note: The transition to using images is not blocked if the witness host is of ESXi version earlier than 7.0 Update 2. However, in this case, after the transition, you use a single vSphere Lifecycle Manager image for the cluster, but you must still use vSphere Lifecycle Manager baselines for the witness host. In such cases, you can use baslines to upgrade the witness host to version 7.0 Update 2, and then you can start managing the witness host with images.
  • You convert an existing vSAN cluster that uses a single image into a stretched cluster with a virtual witness host.
  • You upgrade to vCenter Server and the witness host to version 7.0 Update 3.
You stop using vSphere Lifecycle Manager images to manage the witness host in the following cases:
  • You convert an existing vSAN stretched cluster that uses images into a regular vSAN cluster.
  • You disable vSAN on an existing vSAN stretched cluster that you manage with a single image.
  • You convert the dedicated witness host into a shared witness host.
  • You replace the virtual witness host with a physical server.

Upgrading vSAN Stretched Clusters by Using a vSphere Lifecycle Manager Image

For stretched vSAN clusters, vSphere Lifecycle Manager first upgrades the witness hosts and then proceeds to remediating the hosts in the preferred site and the secondary site. If all the hosts in the preferred site are in a compliant state, then vSphere Lifecycle Manager skips the preferred site and starts remediating the hosts from the secondary site. If any host in the entire cluster is in an incompatible state, remediation stops. For more information about fault domain-aware remediation and the order in which vSphere Lifecycle Manager remediates the hosts in a vSAN cluster, see Using vSphere Lifecycle Manager Images to Remediate vSAN Clusters with Configured Fault Domains.

During remediation, vSphere Lifecycle Manager does not apply to the witness host the full cluster image but only the base ESXi image. That is, vSphere Lifecycle Manager does not install any user components, solution components, or OEM add-ons on the witness host. The hosts in the cluster, however, are remediated against the entire image.

To remediate the witness host against the vSphere Lifecycle Manager cluster image, the following requirements exist:
  • vCenter Server must be version 7.0 Update 3 and later.
  • The witness host must be ESXi version 7.0 Update 2 and later.
  • The witness host must be a virtual server and not a physical server.
  • The witness host must be a dedicated witness host and not a shared witness host.