If Docker runs natively on windows, then why does it need hyper-v

Question

If Docker community runs natively on windows, then why does it need Hyper-v? I.E., doesn't native imply that Docker-Engine can run instructions on windows? It looks to me like it still starts up a Linux VM and runs with-in that.

To me, is seems that docker-toolbox uses an oracle hyper-visor running linux, while Docker community uses Hyper-V running linux. Is there another important difference that I'm overlooking?

Is this correct? Am I understanding the word "native" wrong, is docker mis-using the word, or is there some other aspect I'm missing?

The reason I'm asking, is because I noticed that you don't use Docker-machine with the community edition, and I'm wondering why that is. Is docker-machine the thing that runs natiely on windows, while Docker Engine doesn't? I think the word docker is over-loaded and maybe leads to confusion in this case :)

Thanks in advance!

Answer 1

Docker support for Windows has several variants:

1. Docker Toolbox which includes Docker Machine that will spin up a boot2docker image inside of VirtualBox. These are Linux containers running with a Linux kernel inside the VM. This was originally the only option for Windows users.

2. Docker for Windows using Hyper-V to run the Moby VM, based on LinuxKit, to run Linux images. LinuxKit provides a container based Linux OS, and there's some integration to make it appear less like a VM to the end user, e.g. you can use 127.0.0.1 instead of the IP of the VirtualBox VM. If you have Hyper-V available and want to run Linux containers on Windows, this is the preferred option.

3. Windows Server Containers which run Windows binaries on the same host OS, similar to how Linux containers on a Linux OS do not need a VM.

4. Hyper-V Containers which run Windows binaries inside of a separate VM for additional isolation.

You can read more about the latter two options in Microsoft's docs.

What's important to note is that when you install Docker for Windows on a supported server, like 2016, you have options 2, 3, and 4, that you can toggle between. For Linux and Windows containers, there's a switch in the settings that affects all running containers and commands. And between Windows Server Containers and Hyper-V containers, there's an --isolation option on the docker run command line. So I believe you're required to have Hyper-V support to cover 2 and 4 even if you only want option 3.