vCenter Server High Availability

vCenter Server High Availability or vCenter HA, is one of the most promising feature of vCenter Server 6.5, which provides highest availability for the vCenter Server, without any Microsoft Windows Clustering. Prior to version 6.5, high availability for the vCenter Server could be achieved by means of clustering of Windows based vCenter Server (Supported version was 5.5 and 6.0)and then there was also a product called as vCenter heartbeat which came to its end of life 2014 (for more details on how it is supposed to be achieved with those product and versions, click here).

This feature is available only with vCenter Server Appliance 6.5. It consists of active, passive, and witness nodes that are cloned from the existing vCenter Server instance. It can be enabled, disabled or destroyed at any point in time. It also has a maintenance mode function which prevents any unwanted fail-over during the maintenance window. vCenter HA provides an RTO of about 5 minutes for vCenter Server greatly reducing the impact of host, hardware, and application failures with automatic fail-over between the Active and Passive nodes.

Pre-requisite for setting up vCenter HA.

vCenter Server requirements
  • Requires a single Standard license.
  • Static IP is a must for the vCenter Server management interface.
  • If it does not uses a static IP then the vCenter server appliance needs to be on a host which is part of the same SSO domain(External SSO is a must in this case).
  • The host cluster needs to have 3 hosts at least (recommended).
  • The active vCenter server must be managing the host on which the vCenter Server appliance is hosted.
  • Can be hosted on ESXi 5.5 version or later.
  • Deployment type supported is small (4 CPU and 16 GB RAM) or bigger (Tiny deployment is not supported).
vCenter HA requirements
  • vCenter HA is tested with VMFS, NFS & vSAN.
  • vCenter HA network needs to be different than management network, that is, a separate port.
  • Having HA, DRS and SDRS configured in the environment is highly recommended for Initial placement of VM, VM failover and load balancing of VM where we have the nodes of vCenter HA.
vCenter HA nodes requirement
  • Only Active node will have the Active Management Interface (Public IP to access VC service).
  • The 3 nodes(Active, Passive & Witness) are continuously communicating over a private network which is vCenter HA network.
  • vCenter HA network latency between Active, Passive & Witness node must be less than 10 ms.
  • Active and passive nodes are continuously replicating data.
  • Witness is a lightweight clone of Active node and it provides a quorum against a split-brain situation.

Their are two modes of vCenter HA deployment : Basic and Advanced. vCenter HA is supported with both Embedded and External PSC but there are specific deployment model which is supported for this feature.

Basic mode of vCenter HA

Its a basic workflow designed to run all vCenter HA nodes within the same cluster. This mode will automatically take care off the passive and witness node creation and managing them as well. It will create its own anti-affinity rules, if vSphere DRS is enabled on the host cluster level. Also, it will use Storage DRS for the initial placement the VM. Few customization are possible in this workflow which are : choose specific host, choose specific datastore and choose specific network for each nodes.

Advanced Mode of vCenter HA

Advanced mode is used when you want to place the three nodes that is active, passive and witness nodes to different host cluster, datacenter, vCenter Server. In this workflow the cloning operation has to be performed manually for passive and witness node and to place it on specific datastore with specific IP address.

Basic Mode vs Advanced mode of vCenter HA

Difference between Basic mode and Advanced mode vCenter HA configuration is that advanced workflow model provides more control over the deployment.

vCenter HA cluster Modes of Operation

Option Result
Enable vCenter HA Default mode of Operation which protects from Hardware and software failure. Enables replication between the Active and Passive nodes. If the cluster is in a healthy state, your Active node is protected by automatic failover from the Passive node.
Maintenance Mode Used for maintenance tasks. In maintenance mode, replication still occurs between the Active and Passive nodes. However, automatic failover is disabled.
Disable vCenter HA Disables replication and failover. Keeps the configuration of the cluster. You can later enable vCenter HA again. If the Passive or Witness nodes are lost or recovering from a failure, a vCenter HA configuration can be disabled. The Active node continues as a standalone vCenter Server Appliance.
Remove vCenter HA cluster Removes the cluster. Replication and failover no longer are provided. The Active node continues to operate as a standalone vCenter Server Appliance.

Note: If the cluster is operating in either Maintenance or Disabled mode, an Active node can continue serving client requests even if the Passive and Witness nodes are lost or unreachable.

How synchronization happens between the nodes in vCenter HA.

vcha_transparent

For More reading material.

For more detailed information provided by VMware on vCenter Server HA could be found here : https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.avail.doc/GUID-4A626993-A829-495C-9659-F64BA8B560BD.html

The deployment models supported are described and discussed in depth on this article : https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.avail.doc/GUID-F08F7501-FC06-4A83-806D-89CA489FA3AF.html

To know about the workflow’s please read through the article : https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.avail.doc/GUID-D7AE886A-D1A8-4E4B-A6C0-8E47FAB2D88C.html

For more information on how High Availability was achieved in the older versions of vCenter Server you can go through article : https://kb.vmware.com/kb/1024051

Here is a presentation from VMware which talks about step by step implementation of vCenter HA using Advanced workflow : https://featurewalkthrough.vmware.com/#!/vsphere-6-5/enabling-vcenter-ha-advanced/17

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