On the other hand, the largest VMware customers are logically more conservative and starting migrations from vSphere 5.5 to 6.0 just now, in time of writing this article (beginning of 2017). These large customers have significantly larger scale therefore their PSC/SSO topology is much more complex.
During last few weeks I have discussed some vSphere 6 PSC/vCenter topology design decision points with these customers and I have decided to write down blog post about few useful, publicly available, resources / documents for such discussions.
First and foremost, FAQ below is the most comprehensive VMware KB article about this topic.
FAQ: VMware Platform Services Controller in vSphere 6.0 (2113115)
The most surprised information, even for long time VMware customers, are following two Q&A's from FAQ above.
Q: Can I merge two vSphere Domains together?
A: No, there is no way to merge two vSphere domains together.
Q: Can I get Enhanced Linked Mode (ELM) between two, separate vSphere domains?
A: No, Enhanced Linked Mode requires that all PSCs be in the same domain and replicating. Since two separate vSphere Domains do not have a means of replicating, the new APIs that provide ELM cannot display the contents of both domains.
What does it mean?
Well, if you have multiple independent vSphere 5.5 SSO domains and you want to merge them, you have to do it in vSphere 5.5 before upgrade to 6.0 because you will not be able to do so in vSphere 6 and later.
Note: I do not know how it will change in longer term but it is the true even for vSphere 6.5 which is the latest version in time of writing this blog post.
Q: One of my customers asked me if the same vSphere SSO name (vsphere.local) in their two separate datacenters means that it is the same vSphere domain.
A: No. If you do not have replication between domains, there are not the same domain even they have the same name.
Another good question, you have to ask yourselves is, if you should or should not merge your vSphere domains. The typical reason for single vSphere domain is requirement for Enhanced Linked Mode (ELM). What Enhanced Linked Mode will give you? Below are several benefits of ELM:
- You can log in to all linked vCenter Server systems simultaneously with a single user name and password.
- With Enhanced Linked Mode, you can view and search across all linked vCenter Server systems. This mode replicates roles, permissions, licenses, and other key data across systems.
- You can view and search the inventories of all linked vCenter Server systems within the vSphere Web Client.
- Roles, permission, licenses, tags, and policies are replicated across linked vCenter Server systems.
- You can use WebClient GUI to do cross vCenter vMotion
However, any technology has some limits. In case of vSphere, we should always look at vSphere Configuration Maximums. The relevant information from configuration maximums are
- Maximum PSCs per vSphere Domain - 8
- Maximum PSCs per site, behind a load balancer - 4
- Maximum number of VMware Solutions connected to a single PSC - 4
- Maximum number of VMware Solutions in a vSphere Domain - 10
A VMware Solution is defined as a product that creates a Machine Account and one or more Solution User (a collection of vSphere services) within the VMware Directory Service when the product is joined to the PSC, thus the vSphere Domain. The Machine Account and Solution User(s) are used to broker and secure communication between other Solutions available within the vSphere environment. In order to count against these maximums, the Machine Account and Solution Users must befully integrated with all of the PSC's available feature sets (Identity Management and Authentication Brokering, Certificate Management, Licensing, etc.) such that the product makes full use of the PSC. At this time, only vCenter Server is defined as a fully integrated solution and counts against these maximums. Partially integrated solutions, such as vCenter Site Recovery Manager, vCloud Director vRealize Orchestrator, vRealize Automation Center, and vRealize Operations, do not count against these defined maximums.So vCenters are the only solutions which counts into maximum of 10 VMware solutions.
Now, when you know if you really need and want to merge vSphere domains it must be done in vSphere 5.5 because in vSphere 6 it is not possible.
I was asked by one of my customers, where is written that vSphere domain merging is supported and how it can be done.
Bellow are two very nice blog post written by blogger Thom Greene ...
Merging SSO Domains in vCenter 5.5 part 1: Why?
Merging SSO Domains in vCenter Server 5.5 pt 2: How?
and very detailed blog post of Andreas Peetz referred by Thom in his posts.
Re-pointing vCenter Server 5.5: A Survival Guide to KB2033620
... but resources above are not VMware official documents so where are VMware official documents? Andreas' blog posts are referring to following VMware KB's
Migrating two VMware vCenter Single Sign-On embedded VMware vCenter Servers in the same VMware vCenter Single Sign-On domain (2130433)
How to repoint and re-register vCenter Server 5.1 / 5.5 and components (2033620)
VMware vCenter Server 5.1/5.5 fails to start after re-registering with vCenter Single Sign-On (2048753)