You deploy a plug-in package to the vSphere Client by registering the package as an extension on vCenter Server. When you register your plug-in as an extension on vCenter Server, your plug-in becomes available to any vSphere Client that connects to your vCenter Server.

You must register your plug-in on every vCenter Server where you need to use it. When a vSphere Client connects to a vCenter Server where your plug-in is not registered, the plug-in is not visible to the vSphere Client.

When a vSphere Client establishes a user session to a vCenter Server instance, the vSphere Client application server queries vCenter Server for a list of all available plug-in packages that are registered as vCenter Server extensions. Plug-in packages that are not present on the vSphere Client application server are downloaded and deployed.

The vSphere Client application server can run only one version of each plug-in package. If a plug-in package is present on the application server, but has an older version number than the registered vCenter Server extension, the registered vCenter Server extension replaces the older plug-in package with the newer version.

When vCenter Server instances operate in linked mode, a user login can cause the vSphere Client to upgrade to the latest version of a plug-in. The vSphere Client queries the vCenter Server instance for a list of registered plug-ins, and the vCenter Server in turn queries all other instances in the link group to compare versions of registered plug-ins. The vCenter Server instance then upgrades all its registered plug-ins to the highest version registered within the link group, and presents that version in the user interface. This assures a consistent behavior for plug-ins, regardless of which vCenter Server instance the browser connects to.
Note: When a user views a managed object, the visibility of plug-in object extensions depends on whether the vCenter Server instance that owns the object has an applicable plug-in registered. If so, the vSphere Client always displays the latest version of the plug-in. If not, the vSphere Client does not display the plug-in at all.