Update kubeconfig when creating cluster

[barkbay]

What would you like to be added:

Would be neat that Kind automatically updates the kubeconfig of the user instead of creating a new one that should be imported manually.

Some things to consider:

Patch and merge

One of the tricky part is that we have to patch the kubeconfig as it is provided by kubeadm:

1. host and port must be fixed in order to be used from an external host
2. if we want to be able to merge it into a larger kubeconfig we have to rename the AuthInfo to avoid collisions because kubeadm always uses the key kubernetes-admin. For example we can suffix it with the name of the cluster.

How to do that:

Use the official go client

Pros

• go-client already provides what we need to do that

Cons

• We want to avoid a direct dependency on client-go, it may make Kind harder to depend on in test harnesses

Copy types.go from go-client into the Kind sources

Seems we only need the Config structure from the client-go project.

Pros

• No dependency on client-go
• Config seems stable. De we really care to be not up to date ?

Cons

• It's code duplication
• Could be seen as a dependency because the struct may evolve and we may have to keep it in sync

Import kubeconfig as map[string]interface{}

Pros

• No dependancies

Cons

• Maybe verbose to implement

Make it the default or add a new option ?

Pros

• User friendly, the context is automatically updated

Cons

• How to manage backward compatibility ? Maybe that some existing tools/systems are relying on the current behavior ?

related issues/PR: #113 #512 #520 #517 #790

[BenTheElder]

Thanks for filing this. cc @aojea @neolit123

An additional note is that currently I believe we have an indirect dependency on client-go by way of kustomize, but that could be resolved possibly.

We should also consider the flags and the UX:

• what should the entries be named like? how should we accomplish that?
• should this become the new default?
• how should this feature be toggled?
• what if you lose your kubeconfig file?

[BenTheElder]

I put some more thought into this and looked around at all the feedback and usage I can find and I think perhaps we should both do this and make it the default mode.

More details in #850 which cross references this and a few other issues.

[BenTheElder]

I've mostly implemented this under #850, will PR once some fun cases are handled.

The initial implementation was pretty small and simple, but we need a bit more code to handle with KUBECONFIG is multiple files.

[BenTheElder]

I'm going to fold this into #850 which has more specific details on how to update the UX around kubeconfig.

Also: going the not-client-go route. We recently stopped needing it as a dependency in the command line, and with dropping everything the binary got much smaller and library management got much easier.