Add "kn service apply"

[rhuss]

In what area(s)?

Describe the feature:

One criticism of kn service create is its imperative nature (also I only partially agree as I think at the end we still just create a declarative resource descriptor which is thrown over to k8s)

We have kn service create --force but this (a) not very intuitive and (b) not idempotent (IIRC).

I suggest adding a kn service apply with the very same semantics of a create-and-update that a kubectl apply offers. Having the possibility of a 3-way merge and a distinction of own and external changes for a resource would be nice, but in a first step, I think it might not be necessary (if the implementation is too complicated). The most important part would be to have an idempotent operation (i.e. if applied twice for the same parameters it should be a no-op). kn service apply would be perfectly suited for being used in a CI pipeline step when it's not clear if a service is already deployed or not.

We could have a look at how kubectl apply is implemented. AFAIK its currently done completely client-side but there are plans to move the diff algorithm to the server-side.

[wslyln]

Could I work on this? or is this still be scoped.

[navidshaikh]

/assign @wslyln

I think scope mentioned in the issue description is good to start with.

[rhuss]

@wslyln let me know if you need some more clarification on the scope and use case. Thanks for picking this up !

[wslyln]

Hi sorry, but I don't think I have time right now to accomplish this task, I'll reassign myself if I work on it later. I'll attempted it slightly, but didn't quite understand how the original kubectl apply used annotations to save the previous state's configs.

[rhuss]

No worries, and thanks for the update !

[itsmurugappan]

@rhuss your thoughts on Ko Apply way of dealing this ?
https://github.com/google/ko/blob/master/pkg/commands/apply.go

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[rhuss]

@itsmurugappan I think this would be a nice addition, but only if not restricted to Golang. In the meantime, mink continued on this idea, by leveraging build packs for broader language support. Let's keep core kn focussed on deploy aspects only.