[Parent]: Make containerd default container runtime

[medyagh]

This is to track all the sub issues for all the work needed to change minikube default runtime from cri-dockerd to containerd.

[afbjorklund]

Steps:

1. Change the "--container-runtime" default, from docker to containerd
2. Replace the current nerdctld installation with a dockerd installation
   a) make it socket-activated, like the podman.socket (config upstream)
   b) make it use a unix socket, like the podman.sock (and not TCP 2376)
   c) docker daemon.json: change the snapshotter to use containerd
   d) docker daemon.json: change the containerd namespace to "k8s.io"
   e) need to install a docker client locally, but keep the nerdctl client too
   the "docker" will be like "podman-remote", and "nerdctl" like "podman"
3. Deprecate the docker container runtime option and the docker preload
4. Clean up all the dockershim (<1.24) code that is littering the code base
5. Remove the option to use docker, or alias it to use containerd instead
6. Don't have to maintain cri-dockerd and nerdctld in minikube, anymore

• Deprecate the Docker container runtime and merge with containerd #21841

All references to podman here are just examples, it is used for the CRI-O runtime.
The containerd runtime will still keep the (low-level) ctr and buildctl tools too...

The main difference is that docker-env works remotely, the others have to use ssh:
minikube ssh sudo nerdctl (need to change the containerd namespace to "k8s.io")

---

But changing the default runtime for minikube is a one-line change:

// defaultRuntime returns the default container runtime
func defaultRuntime() string {
        // minikube default
        return constants.Docker
}

Then we can remove Docker container runtime, but keep Docker driver.

        // Containerd is the default name and spelling for the containerd container runtime
        Containerd = "containerd"
        // CRIO is the default name and spelling for the cri-o container runtime
        CRIO = "crio"
        // Docker is the default name and spelling for the docker container runtime
        Docker = "docker"
        // DefaultContainerRuntime is our default container runtime
        DefaultContainerRuntime = ""

The default is just that, and it can reference either of docker or containerd

With this issue, it will change (but existing clusters will keep their current one)

[afbjorklund]

You will also need to update the contributor guide and the process:

https://minikube.sigs.k8s.io/docs/contrib/guide/#contributing-larger-changes

Specifically it is referencing the "MEP", that is no longer being used:

https://github.com/kubernetes/minikube/tree/master/enhancements

[medyagh]

@afbjorklund
I dont think we need to remove cri-dockerd from minikube, it can be one of our available runtimes, just like crio.
changing the default shouldnt have to mean excluding cri-dockerd.

[medyagh]

I think one thing we need to figure out is None Driver with Containerd

[medyagh]

@afbjorklund do you mean elaborating on , why do we need to replace nerdctl with dockered ? does that mean exactly

Replace the current nerdctld installation with a dockerd installation
a) make it socket-activated, like the podman.socket (config upstream)
b) make it use a unix socket, like the podman.sock (and not TCP 2376)
c) docker daemon.json: change the snapshotter to use containerd
d) docker daemon.json: change the containerd namespace to "k8s.io"
e) need to install a docker client locally, but keep the nerdctl client too
the "docker" will be like "podman-remote", and "nerdctl" like "podman"