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. - Why aren’t the vCLS VMs deleted when I disable DRS?
The vCLS VMs are linked to the “cluster object” and not directly to the DRS functionality. Disabling DRS doesn’t impact the vCLS VMs. - 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<identifier>.enabled” and set it to false. 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. - Do I need to do anything for a stretched cluster?
No that is not required, we would recommend however to ensure there’s at least 1 VM in each location from a compute perspective. - 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.
“Can I customize the name of the vCLS VMs?
Today it is not possible to customize the name of the vCLS VM, this has been filed as a feature request and is considered for a future release”
In a lab environment, I was able to rename the vCLS VMs and DRS remained functional. Functionality also persisted after SvMotioning all vCLS VMs to another Datastore and after a complete shutdown/startup of the cluster.
Original vCLS VM names were vCLS (4), vCLS (5), vCLS (6).
New vCLs VM names are now vCLS (1), vCLS (2), vCLS (3).
Does this question, pertain to customizing the names of newly generated vCLS VMs, existing vCLS VMs, or both? Functionality “seems” to be working even though I’ve renamed the generated vCLS VMs in my lab.
Yes you can rename the vCenter entity, but if this VM is for whatever reason deleted by EAM a new VM with a new name with the “vCLS” naming scheme will be created again. Also, you are not supposed to do any ops on the VMs, so renaming is also discouraged. In other words, that it works doesn’t mean VMware will support it 🙂
but it is a valid point, I just updated my post and clarified that section
Also, any impact to rename the vCLS folder?
Yes there could be an impact, I just asked the engineering team and they (right now) advise against renaming the folder!
Another question. Does vCLS currently manage vSAN functions when VC is unavailable?
No
Hope it is in the roadmap
This sounds like steps towards a cluster vCenter, with real cluster FT like availability. Would not be surprised if Corfu was down there 🙂
Nice to have DRS, HA was already distributed, but given the number of solutions that use vCenter as an endpoint, I hope to see full vCenter cluster soon.
Hi Ducan,
how to put all hosts in maintenance mode in a vSAN cluster running vCLS VMs (without having a secondary storage)? The question is about my lab env (but can be interesting also for a prod env).
I’ve 4 hosts with vSAN enabled and sometime i shutdown all the environment.
Before the upgrade to 7U1, to shutdown my env, I turn off all the VMs, put all hosts in maintenance (without data migration) and finally power off the ESXi. Now i’ve some problems to perform a clean shutdown because the vCLS are running on vSAN (seems a chicken egg problem or i missing something)…
In my lab (3 clusters) I simply place all hosts in maintenance mode (one by one) and power them all off, I use the “no data migration” option after I power off all my VMs. It takes a bit of time for the last host to go into maintenance mode, but so far it just works. You are saying that this doesn’t work for you?
Hi Duncan, I just force shutdown the vCLS VM’s and then jump into Maintenance Mode. Quick and dirty. When I bring my lab back up the vCLS VM’s start automatically. What is the impact of doing this, even though the direction from VMware is to never interact with the vCLS VM’s.
I have just tested it 3 times, I do “maintenance mode” from the vCenter UI using “No Data Migration” and it just powers off the VMs running on the vSAN Datastore when I get to the last host.
Hi Duncan, well my vCenter Appliance is on that vSAN Cluster, so I have to shut it down. Trying to enter Maintenance Mode on the ESXi Host interface doesn’t allow you to stop the vCLS VM’s, as it might through the vCenter GUI. Kind of caught be-twixt & between perhaps.
In that situation you should use the “retreat” mode I discussed in this post. It will disable/delete the vCLS VMs, which will allow you to place it in maintenance mode.
Hi Duncan,
yes this doesn’t work for me. Today i changed some configuration on vSAN to have a clean shutdown….
My vSAN is configured with a default storage policy as Erasure Coding with FTT=1, all the VMs and vCLS VMs was configured to using it and with this configuration I’m not able to put the third host in maintenance (i wait about 45 minutes to put the host in maintenance without success). Due to unavailability of some vCLS VMs vSAN storage objects when the second host is put in maintenance, I’m able to power off the vCLS VMs without they can be restarted automatically and then i’m able to put in maintenance the 3rd and 4th Hosts.
Now i changed the vCLS VMs vSAN storage policy with a “simple” FTT=1 (2 mirrors & a witness component), whit this change i can have a clean ESXi maintenance/shutdown. The 3rd host is very slow to reach the maintenance (about 19 Minutes), but the 4th work as expected.
I don’t know if the problem can be related to my env but if not, can be useful have a “maintenance mode” for the vCLS VMs to be able to shutdown it.
One more question, the 3 vCLS VMs are deployed for every vSphere Cluster?
Benja
Are you doing the maintenance mode from the vCenter Server or from the command line? Which “data evac” option did you select?
Via vCenter (deployed on another ESXi outside the cluster) and “data evac” = “No Data Migration”
Is this a shift towards moving to microservices for vCenter or all vmware apps?
Mainly for clustering services right now, but I would expect decoupling to continue!
Why do I have four vCLS machines in my test lab instead of the max of 3 you state?
(vCLS (1), vCLS (2), vCLS (3), vCLS (4))
How many clusters do you have?
There’s two clusters, one management of one host, and one of compute with four hosts.
So you’re implying I’m picking up the forth for the single host management cluster? If I left the single management host out of a cluster, I’d drop to three?
Correct, drop the cluster and that 4th vcls VM will disappear.