In the vSphere 7.0 Update 1 release VMware introduced a new service called the VMware vSphere Clustering Service (vCLS). vCLS provides a mechanism that allows VMware to decouple both vSphere DRS and vSphere HA from vCenter Server. Niels Hagoort wrote a lengthy article on this topic here. You may wonder why VMware introduces this, well as Niels states. by decoupling the clustering services (DRS and HA) from vCenter Server via vCLS we ensure the availability of critical services even when vCenter Server is impacted by a failure.
vCLS is a collection of multiple VMs which, over time, will be the backbone for all clustering services. In the 7.0 U1 release a subset of DRS functionality is enabled through vCLS. Over the past week(s) I have seen many questions coming in and I wanted to create a blog with answers to these questions. When new questions or considerations come up, I will add these to the list below.
- Do I need to maintain/update/manage the vCLS VMs?
No, the VMs are managed by the ESX Agent Manager, you as an administrator should not need to manage these!
- How many vCLS VMs will there be running?
At most, there will be 3 VMs running. If you have 1 host you will have 1 VM, with 2 hosts 2 VMs and with 3 or more hosts you will have 3 VMs.
- What is the resource overhead of the vCLS VMs?
Each VM has 1 vCPU, 128MB memory, 2GB thin disk, no NIC
- If the vCLS has no NIC how does it communicate?
vCLS leverages a VMCI/vSOCKET interface to communicate with the hypervisor.
- On which datastore will the vCLS VMs be provisioned?
It will be provisioned on shared storage, if available during provisioning, otherwise, it will go to local VMFS.
- If one, or more, vCLS VMs are provisioned on the wrong datastore, can I SvMotion it?
Yes, you are allowed to SvMotion the vCLS VMs to a datastore of choice, this should preferably be a datastore which is presented to all hosts in the cluster!
- Can I use Storage DRS (SDRS) to place datastore into maintenance mode which holds vCLS VMs?
SDRS does not consider vCLS VMs for migration, vCLS VMs right now need to be manually migrated, even when using SDRS.
- Can I disable the provisioning of the vCLS VMs?
Yes you can, but keep in mind that vCLS is required for DRS to function. Meaning that if you disable the provisioning of the VMs DRS will not work any longer, which also means that HA can’t leverage DRS for failover placement and will need to resort to the simple placement mechanism.
- I can’t find the advanced setting mentioned in the documentation, what is the setting?
Go to your vCenter Server object, go to the configure tab, then go to “Advanced Settings” and add the key “config.vcls.clusters.domain-c<number>”. The above document describes where to find the domain “c-number” for your cluster.
- Should I create anti-affinity rules for the vCLS VMs?
Right now DRS doesn’t take vCLS VMs into consideration, so an anti-affinity rule would not be considered. After maintenance simply manually move the vCLS VMs to the hosts you want them located.
- Can I create a custom naming scheme for the vCLS VMs?
Today it is not possible to create a custom naming scheme vCLS VM, this has been filed as a feature request and is considered for a future release. We also discourage renaming the VMs at this point in time.
- Can I rename the folder in which the vCLS VMs are stored in the VMs & Templated view?
No, we discourage changing the name of the folder as this could lead to issues when EAM needs to delete VMs.
- Can I login to the vCLS VMs?
Yes, but this is only intended for troubleshooting. This should not be needed during normal operations as these VMs are managed by EAM.
- Does vCLS require Kubernetes for vSphere to be configured?
No, it does not.
- Do I need to back up or replicate the vCLS VMs?
No, there’s no need to create a backup or replicate the VMs. If the VMs are impacted by an outage than HA will restart them or EAM will recreate them automatically.
- Does vCLS work with ESXi on ARM?
No, in the current release vCLS VMs cannot be provisioned to a cluster using ESXi on ARM. You can disable the creation of the VMs following this article.
- If I need to power off my cluster, what do I do with these VMs?
These VMs are migrated by DRS to the next host until the last host needs to go into maintenance mode and then they are automatically powered off by EAM.
- Which data evacuation option should I use when going into maintenance mode cluster wide?
I use the “no data migration” option after I have powered off all normal VMs.
- Is vCLS compatible with Site Recovery Manager (SRM)?
SRM is supported with vCLS starting vCenter Server 7.0 U1a.
- Can I identify these VMs as “special VMs” when automating certain tasks or creating reports through my automation tools?
Yes, you can easily identify them, Niels has listed the properties in this blog article at the bottom.