[Antrea 2.0] Drop support for Docker for Antrea on Windows

[antoninbas]

Describe what you are trying to solve

The K8s documentation lists 2 supported container runtimes on Windows:

• Containerd
• Mirantis Container Runtime (MCR) - a commercial product

Antrea on Windows supports containerd, and we do not claim any support for MCR. We also have a dedicated installation method for Docker (implying Docker CE / Moby, but should work for Docker Desktop as well), leveraging rancher/wins to manage Antrea as a Pod, but should we keep it?

Describe the solution you have in mind

I would like to propose dropping support for Docker on Windows in Antrea v2.0, for the following reasons:

• the industry seems to have overwhelmingly adopted containerd as the container runtime on both Linux & Windows (I imagine that some enterprises that require commercial support may be using MCR)
• rancher/wins doesn't seem to be an active project any more; all commits in the last year or so relate to dependency updates
• the rancher/wins method of managing system components as Pods has been rendered largely obsolete by hostProcess Pods support on Windows. The fact that Docker (AFAIK) does not support hostProcess Pods may be why it is no listed as a supported container runtime in the K8s documentation. Maybe @jayunit100 has some perspective here.

In addition, we have these Antrea-specific reasons:

• we no longer run CI jobs on Windows using Docker as the container runtime, according to @XinShuYang
• we have 3 / 4 supported installation methods for the Antrea Agent on Windows, which can be confusing for users, and dropping one if it's no longer actively used would be beneficial

Describe how your solution impacts user flows

Antrea would no longer officially support Docker on Windows. We would remove instructions specific to Docker from the documentation.

Additional context

The Microsoft documentation lists the following container runtimes as supported on Windows:

• Docker CE / Moby
• Mirantis Container Runtime (MCR)
• Containerd

The script for installing Docker CE still seems to be maintained: https://github.com/microsoft/Windows-Containers/tree/Main/helpful_tools

Docker Desktop is listed as the container runtime for Windows desktop, but:

• Docker Desktop is not free, except for individual and small businesses
• One would expect Windows servers to be used when building K8s clusters

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Anthos clusters on VMware uses Antrea as the CNI for Windows Nodes (dataplane v2). The documentation states:

Containerd and Windows Dataplane V2 are now general availability as of version 1.11.

Docker and Flannel for Windows nodes will be deprecated in a subsequent release. We recommend that you update your configuration now, if applicable, to use containerd and Windows Dataplane V2 instead. See Update Windows Server configuration.

We are currently at version 1.16 of Anthos.

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Even with the removal of dockershim in K8s v1.24, Docker can still be used as the container runtime thanks to https://github.com/Mirantis/cri-dockerd.

[jayunit100]

Yeah this is the right path forward. Host Process containers are better in all ways. Hope we can get ovs to install in a windows pod someday also! Or at least to bootstrap windows components however is needed.

But yeah. I think you'll not find much docker windows antrea need in the windows k8s community.

[antoninbas]

Thanks for the feedback @jayunit100. We recently added a new installation method (for containerd of course) where OVS userspace daemons (ovs-vswitch / ovsdb-server) are run as a Pod, making the installation process simpler.

[antoninbas]

Now that https://github.com/antrea-io/antrea/pull/6019 has been merged, we just need to update the documentation, which I will take care of.