The following is an excerpt from my book Mastering VMware vSphere 5.5, which you can read more on this blog over the coming weeks. To read the full text you can get a copy here. To test out this procedure, download AutoLab.
What is a vCenter linked mode group, and why might you want to install multiple instances of vCenter Server into such a group? If you need more ESXi hosts or more VMs than a single vCenter Server instance can handle, or if you need more than one instance of vCenter Server, you can install multiple instances of vCenter Server to scale outward or sideways and have those instances share licensing and permission information. These multiple instances of vCenter Server that share information among them are referred to as a linked mode group. In a linked mode environment, there are multiple vCenter Server instances, and each of the instances has its own set of hosts, clusters, and VMs.
vCenter Server linked mode uses Microsoft ADAM to replicate the following information between the instances:
- Connection information (IP addresses and ports)
- Certificates and thumbprints
- Licensing information
- User roles and permissions
There are a few different reasons why you might need multiple vCenter Server instances running in a linked mode group. With vCenter Server 4.0, one common reason was the size of the environment. With the dramatic increases in capacity incorporated into vCenter Server 4.1 and above, the need for multiple vCenter Server instances due to size will likely decrease. However, you might still use multiple vCenter Server instances. You might prefer to deploy multiple vCenter Server instances in a linked mode group to accommodate organizational or geographic constraints, for example.
|Item||vCenter Server 4.0||vCenter Server 4.1||vCenter Server 5.0 → 5.5|
|ESXi hosts per vCenter Server instance||200||1000||1000|
|VMs per vCenter Server instance||3000||10000||10000|
Before you install additional vCenter Server instances, you must verify the following prerequisites:
- All computers that will run vCenter Server in a linked mode group must be members of a domain. The servers can exist in different domains only if a two-way trust relationship exists between the domains.
- DNS must be operational. Also, the DNS name of the servers must match the server name.
- The servers that will run vCenter Server cannot be domain controllers or terminal servers.
- You cannot combine vCenter Server 5 instances in a linked mode group with earlier versions of vCenter Server.
- vCenter Server instances in linked mode must be connected to a single SSO server, a two-node SSO cluster, or two nodes in multisite mode.
- Windows vCenter is required. Linked mode is not supported with the Linux-based vCenter virtual appliance.
Each vCenter Server instance must have its own backend database, and each database must be configured as outlined earlier with the correct permissions. The databases can all reside on the same database server, or each database can reside on its own database server.
After you have met the prerequisites, installing vCenter Server in a linked mode group is straightforward. You follow the steps outlined previously in “Installing vCenter Server” until you get to step 10. In the previous instructions, you installed vCenter Server as a stand-alone instance in step 10. This sets up a master ADAM instance that vCenter Server uses to store its configuration information.
This time, however, at step 10 you simply select the option Join A VMware vCenter Server Group Using Linked Mode To Share Information. When you select to install into a linked mode group, the next screen also prompts for the name and port number of a remote vCenter Server instance. The new vCenter Server instance uses this information to replicate data from the existing server’s ADAM repository. After you’ve provided the information to connect to a remote vCenter Server instance, the rest of the installation follows the same steps.
You can also change the linked mode configuration after the installation of vCenter Server. For example, if you install an instance of vCenter Server and then realize you need to create a linked mode group, you can use the vCenter Server Linked Mode Configuration icon on the Start menu to change the configuration.
Perform the following steps to join an existing vCenter Server installation to a linked mode group:
- Log into the vCenter Server computer as an administrative user, and run vCenter Server Linked Mode Configuration from the Start menu.
- Click Next at the Welcome To The Installation Wizard For VMware vCenter Server screen.
- Select Modify Linked Mode Configuration, and click Next.
- To join an existing linked mode group, select “Join a VMware vCenter Server group using
Linked Mode to share information,” and click Next. This is shown in Figure 3.10.
- A warning appears reminding you that you cannot join vCenter Server 5.5 with older versions of vCenter Server. Click OK.
- Supply the name of the server and the LDAP port. Specify the server name as a fully qualified domain name.It’s generally not necessary to modify the LDAP port unless you know that the other
vCenter Server instance is running on a port other than the standard port.
Click Next to continue.
- Click Continue to proceed.
- Click Finish.
Using this same process, you can also remove an existing vCenter Server installation from a linked mode group.
After the additional vCenter Server is up and running in the linked mode group, logging in via the vSphere Client displays all the linked vCenter Server instances in the inventory view, as you can see in Figure 3.11.
One quick note about linked mode: While the licensing and permissions are shared among all the linked mode group members, each vCenter Server instance is managed separately, and each vCenter Server instance represents a vMotion domain by virtue of each vCenter Server having unique datacenter objects that ultimately represent a vMotion boundary. This means that you can’t perform a vMotion migration between vCenter Server instances in a linked mode group. We’ll discuss vMotion in detail in Chapter 12.
Installing vCenter Server onto a Windows Server–based computer, though, is only one of the options available for getting vCenter Server running in your environment. For those environ- ments that don’t need linked mode support or environments for which you want a full-featured virtual appliance with all the necessary network services, the vCenter Server virtual appliance is a good option. We’ll discuss the vCenter Server virtual appliance in the next section.