What's the difference between a VM clone and a template?

Cloning a virtual machine and creating a VM template are similar processes in that they make it easier to build and deploy VMs, but they serve different purposes when it comes to virtual desktop infrastructure.

VDI shops can use templates as the baseline for a mass deployment of production VMs, whereas VM cloning is better suited for testing environments.

One way to think of how VM clones and templates differ is to compare these building blocks to a Microsoft Word document. In Word, you create a document based on a blank template that defines the initial formatting such as margins, type styles and other settings. You can create as many documents as you like off that template, and for each document, you can change the formatting and add whatever text you want. But documents always start at the same place: with the template settings.

A VM clone is like a copy of your Word document. A clone is a copy of another VM at a specific point in time, essentially a duplicate of the last saved version. From there, the copy takes on a life of its own. In the meantime, you can leave the original VM as is, make separate changes or generate more copies. One benefit of using VMware Horizon View for VDI is that it supports clone linking, which keeps the child clone tied to the parent VM and therefore only uses a fraction of the storage that a regular VM would occupy.  

A VM template, on the other hand, is more like the original Word template. It serves as a master version from which you can create many different VMs. The template includes the basic operating system, software and configuration settings. You can then customize the new VMs according to organizational and individual virtual desktop user needs, but all the VMs start from the same source.

It's even possible to generate additional VM templates off the master template to support other work models. IT can also update the master template to patch software or implement new technologies. But it still remains the golden image for creating VMs. For this reason, templates are suited to mass deployments of VMs across production VDI environments.

Clones, on the other hand, are better suited for VDI testing and development environments. Whereas a template serves as a baseline image for creating multiple VMs, a VM clone is an exact copy, sharing many of the hardware and software configuration settings, including unique identifiers, which can create interoperability issues. In VMware vSphere, for example, clones and even VMs used to create clones are not compatible with the vSphere Fault Tolerance feature, which allows a VM to continue operating normally during a component failure. On a small scale, however, clones can be handy for isolating systems and workflows. For example, you can use a VM clone to test an application or service, without putting your original VM at risk.