Only run minikube image build on control plane by default

[afbjorklund]

Currently there is a lot of duplicated code, between minikube image load and minikube image build.

One of these includes selecting which minikube nodes (machines) to run on, in the selected profile that is.

This might have some issues with multi-node:

For load, it will load the image to all the nodes in the cluster (which makes sense, without a registry)
For build, it will build the image on each and every node - which might make less sense, for some builds

For save, it would the save the image from each node in the cluster - which doesn't make so much sense.
The regular assumption is that the same image (name:tag) contains the same content, so only save once ?

The suggestion is to build/save on the Control Plane.

See #11130 (comment) for minikube image save

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This is the single-node workflow:

1. Build image on control plane

When the save functionality is in place, that would be a simple method of loading the new image to the other nodes:

1. Build image on control plane
2. Save image from control plane, to the host cache
3. Load image on worker nodes, from the host cache

When having a registry deployed, or when using an external registry, this becomes the usual cluster workflow:

1. Build image on control plane
2. Push image from control plane, to the registry
3. Pull image on worker nodes, from the registry
   or)
   3a) Save image from registry, in the host cache
   3b) Load image on worker nodes, from the host cache

It would be possible to select another node in the cluster.

  -n, --node='': The node to build on. Defaults to the primary control plane.

Steps 1+2 would be one single command, build.
Same with steps 3, that's also a one-liner load.

As always you have the option of building directly on the host (external to minikube), and saving and pushing from there...
But that would mean that you would always have to transfer the image (even for single-node), instead of rapid turnaround.

[medyagh]

I agree this is a bug ! that is a good idea to build on only on control plane and then load on other thing

[sharifelgamal]

Ideally, we could add a --all flag for when we want to build an image on all nodes instead of just the control plane

[afbjorklund]

Commands:

minikube image build --tag myimage .
minikube image save myimage
minikube image load myimage