kubectl VS client-go

Check https://github.com/kubernetes/kubectl/issues/151

I have read this issue, and up to now it seems not possible to change the kubectl context via an env var: https://github.com/kubernetes/kubectl/issues/1154

However, I would encourage people to take a look at what the code looks like before assuming the Go developer experience on this was positive. Bear in mind that's just the top level kubectl command and some helper functions, the subcommand definitions take up a several more files split into a few more packages. Then you're still not even done, because code that uses the parsed flags still has to redundantly check things that couldn't be enforced at the type level, something Go folks like to pretend is a good thing for some reason.

kubectl is for sure battle tested, but it involves very Kubernetes specific implementations and is going to be too complicated for the first pointer

> context.Background() is typically only used when one doesn’t care about the result. If you did care about the result, you should be passing the parent context to preserve the circuit breaker timeout in case the operation takes too long.

Not necessarily. You would use context.Background in a test situation. It's also commonly used for short-lived applications like a CLI invocation. You can see kubectl uses context.Background quite a lot: https://github.com/kubernetes/kubectl/search?q=context.backg...

> I think the level of pain you experience from mutable references in Rust depends on if you’re coming from an OOP or FP background. I have a FP background and so the patterns I use to build code already greatly restrict mutation. You can usually change code that updates data immutably (creating a new copy of it) with mutable code in rust because the control flow of your program already involves passing that new version back to the caller which also satisfies the borrow checker in most situations.

There has to be a better solution to needlessly copying data.

This is particularly useful for academic purposes, and makes somehow convinient to get the yaml template of k8s objects. I was looking for this as well due to an upcoming ckad test i have. Unfourtunately due to not being considered best practice the request for it was dismissed. https://github.com/kubernetes/kubectl/issues/1073

I see, apologies, I did misunderstand. This is actually a known race condition between kubectl (or even helm, or any Kube API client) issuing the requests to deploy CRs that depend on CRDs while those CRDs are still being installed on the API server. Simply put, kubectl makes these requests too quickly. There is no solution to this currently aside from deploying CRDs separately from the resources they expose. See this kubectl issue: https://github.com/kubernetes/kubectl/issues/1117, and there are some links in the comments to other issues echoing the same problem in helm and elsewhere.

Go add --no-really-all if you really want it: https://github.com/kubernetes/kubectl

You could take a look at how kubectl actually does it: https://github.com/kubernetes/kubectl/blob/master/pkg/cmd/label/label.go

The Kubernetes clients (e.g., Go client) support developers with both methods to connect to a cluster, as we can see in the following examples.

My suggestion would be to start looking at things like https://github.com/kubernetes/client-go first in order to get a feel for the API and how data plane k8s components interact with the apiserver (it's the same thing that kubelet uses). Then move on to trying to build your own k8s operator to get a feel for how people expand and customize k8s functionality without having to modify upstream at all. IMO the codebase itself is too messy and in constant flux to make too much sense of it unless you are planning to contribute to upstream.

GitHub related issue https://github.com/kubernetes/client-go/issues/735

CUE is cool and all but as soon as I start writing real code structures I want to reach for client-go.

I'm... really not sure I agree with this, from a philosophical point of view. It feels like this is making "eh, we'll just upgrade our Go version next quarter" too easy; ultimately some responsibility toward updating your application's Go version to work with what new dependencies require should fall on Us, the application developers. Sure, we're bad at it. Everyone's lived through running years-old versions of some toolchain. But I think this just makes the problem worse, not better.

Its compounded by the problem that, when you're setting up a new library, the `go` directive in the mod file defaults to your current toolchain; most likely a very current one. It would take a not-insignificant effort on the library author's part to change that to assert the true-minimum version of Go required, based on libraries and language features and such. That's an effort most devs won't take on.

I'd also guess that many developers, up-to this point if not indefinitely because education is hard, interpreted that `go` directive to mean more-of "the version of go this was built with"; not necessarily "the version of go minimally required". There are really major libraries (kubernetes/client-go [1]) which assert a minimum go version of 1.20; the latest version (see, for comparison, the aws-sdk, which specifies a more reasonable go1.11 [2]). I haven't, you know, fully audited these libraries, but 1.20 wasn't exactly a major release with huge language and library changes; do they really need 1.20? If devs haven't traditionally operated in this world where keeping this value super-current results in actually significant downstream costs in network bandwidth (go1.20 is 100mb!) and CI runtime, do we have confidence that the community will adapt? There's millions of Go packages out there.

Or, will a future version of Go patch a security update, not backport it more than one version or so, and libraries have to specify the newest `go` directive version, because manifest security scanning and policy and whatever? Like, yeah, I get the rosy worldview of "your minimum version encodes required language and library features", but its not obvious to me that this is how this field is, or even will be, used.

Just a LOT of tertiary costs to this change which I hope the team has thought through.

[1] https://github.com/kubernetes/client-go/blob/master/go.mod#L...

[2] https://github.com/aws/aws-sdk-go/blob/main/go.mod

I looked at dynamic package, but it seems like it needs GroupVersionResource, which is different for, say, Service objects and Deployment objects. Also when I pass schema.GroupVersionResource{Group: "apps", Version: "v1"} it doesn't find anything, when I pass schema.GroupVersionResource{Version: "v1"} it finds only namespace object and also doesn't looks for labels, though I provided label options:

I'm writing a script that uses the k8s.io/client-go library (godocs here) to manipulate Deployments. In particular, I want to add a label selector to every Deployment in my cluster. Deployment label selectors are immutable. So my approach is to:

Actually, kubebuilder is not using the standard Go libraries, but one using reflection to dynamically resolve the client based on the type you hand it (which is arguably better). The "official" client is k8s.io/client-go.

Then on June 18th, 2022, I got a chance to meet our mentors and the other mentee of OpenELB (the mentee and the mentors of OpenFunction were also there). There I was informed about how to start working on the project, so I started learning about using the Kubernetes API client. After experimenting with the official Kubernetes Client, I learned that it's not very feasible to use that for dealing with CRDs (custom resource definitions), so I explored the controller-runtime client as per what I found in many sources, and found that it was a great fit for the backend of our project. During that time, I also built a simple project to see if everything would work as expected or not (as this was the first time I dealt with a Kubernetes client, I considered that debugging would be easier in a smaller project).