velad create clusters should support linux

[wonderflow]

https://github.com/kubevela/velad/blob/main/docs/02.multicluster.md

It's only support macos and windows for now.

[chivalryq]

Multicluster is provided for user to experience. This feature make it easy to develop app and try multicluster in mac/windows. But on Linux, deployment is more than development. I don't think this is nessesary.

We are using K3s in VelaD when velad install in Linux. If we have to do this, we can:

1. switch to K3d in Linux VelaD
   pro: unify all system, simplify the VelaD.
   con: may lose some performance in Linux

2. include both K3d and K3s in Linux VelaD. Use K3d when create non-default cluster
   pro: no performance problem if only use default cluster.
   con: much complex network problem.

Either give up performance, or make VelaD too complex and huge.

In summary, I don't think this is nessesary for now.

[wonderflow]

Make sense

[webwurst]

I would like to try out the multicluster features of KubeVela on Linux. That's the reason I came to this repo :) And I am fine with K3d for this, even when it means downloading it as a separate binary.

[charlie0129]

I would like to see k3d in Linux too. It will be convenient since I use Linux as my daily development machine.

Currently k3s is a major block preventing me from even installing velad at the first place. (k3s is not compatible with my root filesystem ZFS) Switching to k3d can solve this problem.

I think the users of velad are mainly new users or developers. They use velad to try out / develop KubeVela, i.e., they use velad in a development environment, so performance doesn't matter much. If they want to deploy KubeVela in production, mostly likely they already have several existing production clusters.

So in my opinion, development is still a major use-case over deployment for velad, even in Linux.

[chivalryq]

In fact, velad is basically a tool for development and try out for now. It's hard to guarantee the production-level availability in such tool.

For those who wanna build production cluster using k3s, there are also instructions in K3s document. Let's keep velad simple and remove K3s component in velad. Unifying the user experience also helps to make VelaD the best tool to experiment KubeVela and even cloud-native application delivery.

What do you think of this? @wonderflow

[wonderflow]

@chivalryq I think we should support k3d for linux. All requests in this issue all running velad as developer environment but they can't work smoothly.