VCHA

Maximum number of vCenter Servers per Single Sign-On (SSO) Domain

03.29.2017 by William Lam // 9 Comments

This particular question and its variations have been raised quite a bit lately by our field and customers. For me, this was an opportunity to see if we can provide some additional clarification and help explain some of the nuances that may have been causing some of the confusion around the supported maximums for both vCenter Server and the Platform Services Controller (PSC).

In the vSphere 6.5 Configuration Maximum, there are three specific maximums that helps us answer our question on the maximum number of vCenter Servers per vCenter Single Sign-On (SSO) Domain. I will go through each of the maximums and provide some additional context that will help us derive the answer to our question.

The first is the "Linked vCenter Servers" which defines the maximum number of vCenter Servers that can be supported in an Enhanced Linked Mode (ELM) configuration. What is interesting about this particular maximum is that it actually answers the majority of our question. By definition, an ELM consists of a single SSO Domain. This then means that you can only have a maximum of 10 vCenter Servers per SSO Domain.

vCenter Server Maximum

Configuration	Maximum
Linked vCenter Servers (w/External PSC)	10
Linked vCenter Servers (w/Embedded PSC)	15

Note: As of vSphere 6.7, you can have up to 15 Embedded VCSA's within an ELM.

The second is the "Maximum PSCs per vSphere Domain" which defines the maximum number of PSC's that can be part of a single SSO Domain, pretty straight forward. The third is the "Maximum PSCs per site behind a load balancer" which just adds an additional constraint when using a load balancer with your PSCs.

Platform Services Controller Maximum

Configuration	Maximum
Maximum PSCs per vSphere Domain	10
Maximum PSCs per site behind a load balancer	4

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vCenter Server High Availability (VCHA) PowerCLI 6.5 community module

12.08.2016 by William Lam // 15 Comments

As some of you may know, I have been spending some time with the new vCenter Server High Availability (VCHA) feature that was introduced in vSphere 6.5. In fact, I had even published an article a few weeks back on how to enable the new vCenter Server High Availability (VCHA) feature with only a single ESXi host which allowed me to explore some of the new VCHA APIs without needing a whole lot of resources to start with, obviously, you would not do this in production 🙂

For those of you who are not familiar with the new VCHA feature which is only available with the vCenter Server Appliance (VCSA), Feidhlim O'Leary has an excellent write up that goes over the details and even provides demo videos covering both the "Basic" and "Advanced" workflows of VCHA. I highly recommend you give his blog post a read before moving forward as this article will assume you understand how VCHA works.

In playing with the new VCHA APIs, I decided to create a few VCHA functions which I thought would be useful to have as a PowerCLI module for others to use and also try out. With that, I have published my VCHA.psm1 module on the PowerCLI Community Repo on Github which includes the following functions:

Name	Description
Get-VCHAConfig	Retrieves the VCHA Configuration
Get-VCHAClusterHealth	Retrieve the VCHA Cluster Health
Set-VCHAClusterMode	Sets the VCHA Cluster Mode (Enable/Disable/Maintenance)
New-VCHABasieConfig	Creates a new "Basic" VCHA Cluster
Remove-VCHACluster	Destroys a VCHA Cluster

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How to enable vCenter Server High Availability (VCHA) in vSphere 6.5 w/single ESXi host?

11.16.2016 by William Lam // 5 Comments

One of the big new features that was introduced in vSphere 6.5, exclusively for vCenter Server Appliance (VCSA), is the vCenter Server High Availability (VCHA) capablilty. Feidhlim O'Leary has an excllent blog post covering what VCHA provides as well as a couple of demo videos on how it works, definitely worth checking out! After upgrading one of my home lab enviornments to vSphere 6.5, I wanted to try out this feature from an educational standpoint and specifically around using new VCHA vSphere APIs.

Like most vSphere Home Labbers, I have limited hardware and if you try to enable VCHA with only a single ESXi host, you will see the following error:

This operation would violate a virtual machine affinity/anti-affinity rule.

As you might expect, VCHA will automatically provision affinity rules to ensure that the active, passive and witness node are not all running on the same physical ESXi host. For a production deployment this is completely valid but for lab and testing purposes, this might be a tough requirement to satisfy. I was hoping there might be an override option and searching for the word "ha" in the vCenter Server Advanced Settings lead me to an interesting property called config.vpxd.vcha.drsAntiAffinity. This discovery was purely by luck and I had noticed it was set to true by default, so I decided to change it to false and see what would happen.

To my surprise, changing this setting worked and I was able to successfully enable VCHA in my lab with all three nodes just running on a single ESXi host 😀

An alternative solution would be to deploy a 3-Node Nested ESXi cluster which would not require this modification, but my physical ESXi host was limited on memory, only 16GB and would have been a lot slower.