While nesting a VMware ESXi hypervisor inside another VMware product like Workstation, Fusion, or vSphere may be possible, doing so in a production environment probably isn't the best solution (that's me trying not to use the word "crazy"), and it definitely shouldn't be considered a supported architecture for an organization.
But the lack of official support from VMware has never slowed down the exploratory minds of the VMware community. These individuals work together to make the impossible possible, and they're always looking for the next thing to make virtualization life easier and more productive.
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What exactly do we mean when we talk about "nesting"?
Basically, it means VMware vSphere can be virtualized within itself. In other words, you can install and operate the VMware ESXi hypervisor within a virtual machine running inside another hypervisor environment such as VMware vSphere.
This can be a great tool for learning about VMware software, performing demonstrations, experimenting with and testing new features and configuration arrangements, and upgrading to new releases without needing extra dedicated physical hardware that you may not have on hand. If you're running a home lab, for example, nesting could prove extremely beneficial. Many virtualization administrators are doing just that.
Case in point, the nested virtualization forum on the VMware Community site has proven to be quite popular and has seen its share of activity over the last 12 months. As an example of how attractive this capability has become, a single post from two months ago titled "Running Nested VMs" has already been viewed more than 152,000 times and has received more than 50 responses by community members. Beyond VMware's own products, many of these same users are experimenting with and sharing ideas around nesting a VMware ESXi environment within competitive hypervisor products such as Microsoft Hyper-V, XenServer, and KVM.
While nesting has proven popular within the VMware community, it hasn't been without complaints. One of the major hangups has been the fact that you couldn't install VMware Tools within the VM running ESXi. VMware's tools provide additional drivers and capabilities for interaction between the guest and the host, and without it, the experience isn't all it can be. The community has been searching for an answer to that challenge, which brings us to one of the latest new free tools from VMware.
As is often the case with this type of community push and end-user inquiry, VMware engineers have been hard at work creating a number of quick hit, free VMware product enhancements known as Flings. These free yet unsupported tools are created by a division of VMware known as VMware Labs. The lack of official support from VMware for the use of these tools in a production environment hasn't slowed down their success or interest from virtualization administrators.