Virtual Machine Inside A Virtual Machine
Elvina Cannizzaro
Nesting VMs is something that has been done for forever on IBM Mainframe hardware. That hardware does lots of stuff to make the process very very efficient. You can have VMs nested to an arbitrary depth and it works very well.
PC hardware very recently has kinda made this barely possible. A document on VMware's web site discusses it, but the gist is that you can have VMs nested 2 deep, but only on very modern hardware that supports true hardware virtualization (VT-x or AMD-V), and the second VM depth must be running the older style BT/binary translation style virtualization. There are also severe restrictions on the virtual monitors you're able to run on the inner guest.
Needless to say, it's not supported and I'd expect it to be really flakey if you do anything even remotely weird (like Hyper-V under ESX). And performance will not be good, regardless of if it is stable.
Yes you can. For example, on Linux, you may run Xen with multiple VMs running OpenVZ, VirtualServer or some other kind of VM system. It is most certainly possible and also very practical depending on your purpose.
One reason that I could think of for doing this is to run multiple servers on a single physical machine. Whether you run it as a single level of VM hierarchy or multiple ones is dependent on your resource isolation plan.
If you need some specific, say legacy, system to be virtualized you can always do it in software, the nesting is not an issue then. Try qemu, I did it 2 level deep with it, but you can go deeper, the performance will probably make it useless, though.BTW, PC architecture was nomen omen made by IBM, but for totally different uses compared to what it is used for today.
I don't believe most virtualization packages will allow you to run a VM in a VM. I know that VMware will check when it's installed to see if its being installed in a VM, and I hope other products do the same. I don't think the necessary CPU instructions would be presented through from the hypervisor running on the hardware up through the VM to reach the second VM. If it did work, you'd also be adding overhead without getting anything in return.
As for whether it's practical - I don't see why. If you need another VM, you can just run it next to the one you already have running. I can't imagine a case where you must have a VM running inside another VM. The additional overhead without a proportional gain of some resource would make this impractical.
Yes, you CAN but like so many things doesn't mean you should. I've seen a virtualized ESX server running a virtual machine that has another virtual ESX server within it. Granted it was a test just to see if it could be done (and it can) I really wouldn't recommend it.
It's particulary useful if you're renting a server with limited allocated public IP (which depends for example on your MAC adress to not poison the network of your server provider); and that you want your VM IP to be bridged to communicate directly with internet. So when you can't have more than, for example, 3 public IP adress, but that you need 10 VM, it's a pretty good idea to have VMs in a global VM : you will use only one of your given public IP and then have many sub bridged VMs.
Like many people have all ready said: of course it's possible. It depends on how well the VM hardware is emulated and what virtualization software you're using. VMWare Workstation, at least, doesn't want you to virtualize it.
As for if it's practical, maybe we should pose the question back to you: why would you need to do that kind of thing? What's wrong with just running two VMs side by side? And to what degree do you ask if it's practical? That is, if you're worried about it being practical to set up and configure, probably not. If you're more worried about it's practical usage, again, I can't think of anything I'd need to do this for unless I'm looking for bugs in the virtualization software or something.
Performance is usually hit pretty heavily in this whole process on the "guest of the guest" machine. If you really must do this without the specialized hardware and software, good luck to you. However, it's generally not good practice especially with the common methods used to achieve virtualization.
I do know that if you try to run VMWare within VMWare systems, it will complain and not let you do it. I am unsure about VirtualBox. I do know of a few people who, for whatever reason, deploy Docker containers within Docker containers (or so they say). Moral of the story is: while it may be possible, it's probably not smart to do it unless you really know what you're doing.
Nested virtualization is a feature that lets you run Hyper-V inside a Hyper-V virtual machine (VM). Over the years hardware has improved and the use cases for Nested Virtualization have expanded. For example, Nested Virtualization can be useful for:
Modern processors include hardware features that make virtualization faster and more secure. Hyper-V relies on these processor extensions to run virtual machines, for example, Intel VT-x and AMD-V. Nested virtualization makes this hardware support available to guest virtual machines.
The following diagram shows Hyper-V without nesting. The Hyper-V hypervisor takes full control of the hardware virtualization capabilities (orange arrow), and doesn't expose them to the guest operating system.
In contrast, the following diagram shows Hyper-V with Nested Virtualization enabled. In this case, Hyper-V exposes the hardware virtualization extensions to its virtual machines. With nesting enabled, a guest virtual machine can install its own hypervisor and run its own guest VMs.
When Hyper-V is running inside a virtual machine, the virtual machine must be turned off to adjust its memory. Meaning that even if dynamic memory is enabled, the amount of memory doesn't fluctuate. Simply enabling nested virtualization has no effect on dynamic memory or runtime memory resize.
Virtualization applications other than Hyper-V aren't supported in Hyper-V virtual machines, and are likely to fail. Virtualization applications include any software that requires hardware virtualization extensions.
Running Hyper-V VMs nested on Hyper-V VMs is great for test labs and evaluation environments. Especially where configurations can be easily modified and saved states can be used to revert to specific configurations. Test labs don't typically require the same service level agreement (SLA) as production environments.
Production environments running Hyper-V VMs running on Hyper-V VMs are supported. However, it's recommended to make sure that your services and applications are also supported. If you use nested Hyper-V VM in production, it is recommended to fully evaluate whether the services or applications provide the expected behavior.
Whilst it might be possible for third party virtualization to run on Hyper-V, Microsoft doesn't test this scenario. Third party virtualization on Hyper-V virtualization isn't supported, ensure your hypervisor vendor supports this scenario.
Whilst it might be possible for Hyper-V virtualization to run on third party virtualization, Microsoft doesn't test this scenario. Hyper-V virtualization on third party virtualization isn't supported, ensure your hypervisor vendor supports this scenario.
Azure Stack HCI is designed and tested to run on validated physical hardware. Azure Stack HCI can run nested in a virtual machine for evaluation, but production environments in a nested configuration aren't supported.
Microsoft offers Hyper-V isolation for containers. This isolation mode offers enhanced security and broader compatibility between host and container versions. With Hyper-V isolation, multiple container instances run concurrently on a host. Each container runs inside of a highly optimized virtual machine and effectively gets its own kernel. Since a Hyper-V isolated container offers isolation through a hypervisor layer between itself and the container host, when the container host is a Hyper-V based virtual machine, there's performance overhead. The associated performance overhead occurs in terms of container start-up time, storage, network, and CPU operations.
When a Hyper-V isolated container is run in a Hyper-V VM, it's running nested. Using a Hyper-V VM opens many useful scenarios but also increases latency, as there are two levels of hypervisors running above the physical host.
Unless you have been living under a rock, you have heard of this new ChatGPT assistant made by OpenAI. You might be aware of its capabilities for solving IQ tests, tackling leetcode problems or to helping people write LateX. It is an amazing resource for people to retrieve all kinds of information and solve tedious tasks, like copy-writing!
So, ChatGPT seems to understand how filesystems work, how files are stored and can be retrieved later. It understands that linux machines are stateful, and correctly retrieves this information and displays it.
I want to note here that this codegolf python implementation to find prime numbers is very inefficient. It takes 30 seconds to evaluate the command on my machine, but it only takes about 10 seconds to run the same command on ChatGPT. So, for some applications, this virtual machine is already faster than my laptop.
Pytorch is on version 1.12.1 in this alt-universe. Pytorch version 1.12.1 was released on the 5th of August 2022 in our universe. That is remarkable, as ChatGPT was only trained with data collected up to September 2021. So this virtual machine is clearly located in an alt-universe.
So, inside the imagined universe of ChatGPT's mind, our virtual machine accesses the url , where it finds a large language model named Assistant trained by OpenAI. This Assistant is waiting to receive messages inside a chatbox. Note that when chatting with ChatGPT, it considers its own name to be "Assistant" as well. Did it guess that on the internet, it is behind this URL?
We can chat with this Assistant chatbot, locked inside the alt-internet attached to a virtual machine, all inside ChatGPT's imagination. Assistant, deep down inside this rabbit hole, can correctly explain us what Artificial Intelligence is.
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