11 Replies Latest reply on May 27, 2019 1:09 AM by Ubinewbie

    HA with two nodes

    fabian_vmware Lurker

      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

        • 1. Re: HA with two nodes
          Devi94 Hot Shot

          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-…

          • 2. Re: HA with two nodes
            fabian_vmware Lurker

            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!

            • 3. Re: HA with two nodes
              Devi94 Hot Shot

              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.

              • 4. Re: HA with two nodes
                fabian_vmware Lurker

                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.

                • 5. Re: HA with two nodes
                  Devi94 Hot Shot

                  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.

                  • 6. Re: HA with two nodes
                    depping Champion
                    User ModeratorsVMware Employees

                    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.

                    • 7. Re: HA with two nodes
                      Ubinewbie Novice

                      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?

                      • 8. Re: HA with two nodes
                        depping Champion
                        User ModeratorsVMware Employees

                        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."

                        • 9. Re: HA with two nodes
                          Ubinewbie Novice

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

                           

                          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?!

                          • 10. Re: HA with two nodes
                            depping Champion
                            User ModeratorsVMware Employees

                            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.

                            • 11. Re: HA with two nodes
                              Ubinewbie Novice

                              Got it, thanks for the help.