HA with two nodes

[fabian_vmware]

Hello,

I am experimenting with VMware vSphere and High Availability for days now. And I am a bit confused from the documentation, maybe my question is very simple and one of you can give me a short answere.

When I create a 2-node HA Cluster, is this possible to be handled with two physical mashines? When reading the documentation, I thought so... but in the end I need a third physical server as a wittness, right?

Thanks!

Fabian

[Devi94]

for a production environment, you must need 3 esxi hosts. for test/home lab, you can follow below article to deploy with single/two esxi hosts

https://www.virtuallyghetto.com/2016/11/how-to-enable-vcenter-server-high-availability-vcha-in-vsphere-6-5-wsingle-esxi-…

[fabian_vmware]

Hello!

thank you for the answere. What do you mean by ESXI Host? This is one thing I get confused in the documentation. A host ist not mandatory to be a physical server, I could create a host in a virtual mashine.

So when I create my Test-environment with two physical machines. I would install the witness inside a VM on one of the physical machines. But this way I cannot test / reproduce HA. When I switch off one of the physical machines the system is not be able to work.

So basically, what my question ist. Can I setup HA with only 2 physical servers? I guess not?

Thank you!

[Devi94]

ESXi is your physical server where hypervisor is running. If you have two physical servers, primary can run on one and peer and witness can run on second. So when you bring down your primary vcenter, peer will come online. for doing this with two physical servers, you need to disable value as mentioned in article.

[fabian_vmware]

Thank you!

but in this scenario, when my secondary physical server crashes (with the witness installed aswell) the whole system crashes. So with only two physical servers, I do not have redundancy, I still have a single point of failure. The only advantage would be, if Server 1 crashes, Server 2 (with the witness) can handle the tasks.

[Devi94]

as i said this is only for home lab, if you want to use full functionality you need 3 physical boxes. to answer your question,

can this be implemented with 2 servers ? yes it can be.

if you want complete functionality, you must need 3 servers.

[Duncan Epping]

it would be a bit easier to answer if you use the right terminology. you posted this in the vsphere HA section, but it appears you are asking about vCenter HA.

If you are indeed asking about vCenter HA then the answer is that you need 3 physical machines, of course you can run it on less than 3 but if the host fails which holds two out of three than you lose quorum and the failover most likely will not work. Detailed info can be found here: https://blogs.vmware.com/vsphere/2018/04/vcenter-high-availability-deep-dive-part-1.html

If you are talking about vSphere HA then the answer is that you need 2 physical machines. vSphere HA works with just 2 machines, and there's no witness needed.

[Ubinewbie]

With regards to vCenter HA, what if you had 2 physical hosts and you kept both the witness and passive node together on one host, but the active node on the other.

So if the host with the active node goes down, you have the passive and witness still up on the other host - therefore failover occurs successfully?

And if the host with the passive & witness node goes down, failover doesnt occur, but your active node is still up and therefore vCenter is still available?

[Duncan Epping]

he is talking about vSphere HA first of all, secondly when it comes to ANY highly available design, it is never a good idea to run a witness on the same host as one of the components of a cluster. If that host goes down then the vCenter will also be down as a result. This is described in this paper on page 5:

https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/vcha65-perf.pdf

"More than one node fails or is isolated: – This means all three nodes—Active, Passive, and Witness—cannot communicate with each other. This is more than a single point of failure and when this happens, the cluster is assumed non-functional and availability is impacted because VCHA is not designed for multiple failures."

[Ubinewbie]

Yes I know, however Google sent me here and in your reply you mentioned vCenter HA which is what I was interested in :smileyhappy:

This is actually a real world deployment where I'm working within certain constraints, 2 physical hosts being one of them, I understand in an ideal world the witness should be independently held but this is what I'm working with.

Thanks for the reference, interesting, so you're saying that if the passive & the witness node are both unavailable, the active node does not operate even though it is still up/alive?!

[Duncan Epping]

This is actually a real world deployment where I'm working within certain constraints, 2 physical hosts being one of them, I understand in an ideal world the witness should be independently held but this is what I'm working with.

if that is what you are working with, then just do a single instance vCenter Server. if the wrong host fails vCenter will be unavailable. If you just use vSphere HA and shared storage you have a better availability story than you describe above.

[Ubinewbie]

Got it, thanks for the help.