Kubernetes CRDs (Custom Resource Definitions) and CRs (Custom Resources) explained, with examples 

Hi Andrei, First of all thanks for the appreciation, I really appreciate it. Those are great set of questions that you asked. Let me try to answer them one by one 1. This thing is explained very well in the book "Programming Kubernetes" at the very start of the chapter 4. So first steps/layer (aggregator) is responsible to reply for the resources that are introduced by writing a custom API Server (we can do that). If the resource that we requested is not there, the request will be forwarded to another layer that responds for the k8s native objects and if the resource are not found there as well, apiextensions will, that is responsible to respond for CRDs will respond. If even api extensions is not able to respond to the resource, client would get 404. 2. Per my understanding (I might be a bit off here), If the resource is persisted in the etcd in that case administrator will have to somehow migrate the resource, but client-go library that we use to talk to API Server should be able to do the conversion on the fly. So if a resource is available in two versions, let's say v1beta1 and v1, and that resource is created using apiVersion v1beta1, we would be able to get that by apiVersion v1 as well. Or in other words that resource would be available in apiVersion v1 as well. 3. Subresources are as the name suggests another nested endpoints to main resources, for example logs are not resources but pods' logs can be requests by calling logs sub resouce on pod resources. So the endpoint would look somewhat like /api/v1/namespace/namespace/pods/name/logs If you have a resource that is being handled by a controller once the things, that a controller is supposed to do, are done; it (controller) should be able to update the status for the resource. And that is where subresource comes into picture. If we introduce sub resource for ETCD CRD let's say, in that CRs for ETCD are going to have status sub resource that can be updated by controller/operator. This again is explained in great detail in the same book same chapter, under heading Status Subresource. I hope this helps, let me know if something else needs to be discussed. I would be happy to discuss that. Another thing that I wanted to ask is, can post you comment on my twitter with you name, this is really a great comment Andrei.

​@@viveksinghggits Thanks for your reply, really appreciate it. I'll definitely check out the book you mentioned. I've been reading "mastering Kubernetes" and been also considering to look into "Kubernetes in practice" but I guess now you convinced me to also have a look at "Programming Kubernetes". Regarding twitter, sure. Just let me know your twitter ID (maybe you want to add to your video descriptions?).

Hey 👋, I am at viveksinghggits on Twitter.

Ohh damn, If I re-read the comment again, that is not what I meant. I wanted to ask your permission to tweet this screenshot.

@@viveksinghggits I was trying to create CRD for OpenShift Container Storage which contains worker node info and provisioner details. Can I get help on it?

Thank you. I am glad it helped.

Hey 👋, Thanks Nitesh, I really appreciate it. 🙏

Thank you.

Thanks for watching Suresh.

Haha, thanks Rayehan. I appreciate 🙏 it.

Hi 👋 Payal, Thank you for the kind words, I appreciate it.

Thank you for watching.

Hey 👋, Thanks Hashil, I am glad it was helpful.

@@viveksinghggits very much helpful. keep going

Sure, thank you.

Hey 👋, Thank you.

I am glad it helped.

Thanks Ofer

Thank you for watching.

Thank you.

Thank you 😊

Thank you 😊

Thank you 😊.

Hey 👋, Thanks Manas.

Thank you.

Damn. Thanks Shikhar 😊🙏 I really appreciate it.

Thank you

Thank you.

Thank you 😊.

Hi Emma, Thank you for the kind words. I am assuming you meant writing an operator for the custom resources, if yes, I already have a video where I wrote a controller/operator for custom resource. If you meant something else, can you please explain what exactly you meant by add logic to CRD.

This is the video about custom controller that I talked about Writing K8S Operator (Kluster): ru-vid.com/group/PLh4KH3LtJvRTtFWz1WGlyDa7cKjj2Sns0

Thank you

Thank you.

I am glad you liked them 😊

@@viveksinghggits next video this topic out yet?

I am planning to make a video on setting up a kubernetes cluster using kubeadm.

Hey 👋, Thanks Orry.

Hi Madhur, While registering new resources using CRD, we can configure if the new resource is going to be namespace scoped or cluster scoped. Like the name suggests if a CRD is registering a CR that is namespace scoped, it would mean that when we create the new resource we can specify which namespace that new resource should be created in. Similarly cluster scoped resource is not contained within a namespace like storage class etc. In other words it’s not different from how Kubernetes native cluster and namespace scoped resources behave.

Hi Moudjer, Thank you. I don't have plans right now, to make that video but let's see if I can create one in future.

Hi Rohan, I am not very comfortable with CRCs, so I don't have a plan to make that video. I am assuming you are talking about code ready containers.

Sorry, i meant custom resource controllers.

I think this is what you are talking about Writing K8S Operator (Kluster): ru-vid.com/group/PLh4KH3LtJvRTtFWz1WGlyDa7cKjj2Sns0

Hi Parshuram, You can specify the port to kubectl proxy command using --proxy flag. So if there is something already running on port on your machine you can always use another port using above mechanism. More details are here kubernetes.io/docs/tasks/extend-kubernetes/http-proxy-access-api/#exploring-the-kubernetes-api Let me know if this doesn't help.

Hi Pawan, I didn't understand the question correctly. What do you exactly mean by add custom resource to existing pod interface? Also, later you asked if custom controller would be able to update the pod status, the answer is yes. As long as the controller has authz to update the status, it should be able to.

Hey Rajat, I am assuming you want to update a specific field of a custom resource using kubectl. One thing I can think of right now is, creating a kubectl plug-in that would take members value and custom resource name and update the resource with the given value.

@@viveksinghggits I want to update using kubectl patch command

Aah makes sense. Did you try doing that, what is the problem? I don't remember the command ready.

@@viveksinghggits something like this kubectl patch crd functions -n default --patch '{"spec":{ InvokeStrategy: 5 }}'

Hi Athiq, I usually push the code that write in the videos but I think I don't push the manifests. Maybe I will try to do that in coming videos.

Can you mention the timestamp please. Where exactly I am talking about member.

@@viveksinghggits its present in crd configuration file members: 3 like this

Do you want to talk about it, in a Twitter space?

@@viveksinghggits Not right now, but yeah, I am up for talking about k8s.

Sure, whenever. I am not challenging you or anything. Its just that I would understand your point of view and opinion. What's your Twitter handle?

Hey Rene, I am sorry about that, yeah the handwriting is not readable, it's bad. I usually try to not write important things there. But I will try to make that better for sure. Thank you.

@@viveksinghggits Thanks your reply. I really had problems to decode your writing. Maybe you can type a bit more. Anyway, good video and explanation nevertheless! 👍

Thanks Rene, I appreciate it. Yeah, I will try to type more and improve writing as well.

Hi Shams, That's not really a useful feedback. I don't know what should I do about your comment. 1. Is the audio quality too bad? 2. Is the way I speak is so bad that you are not able to understand 3. Or the sentences that I am saying are not making any sense

@@viveksinghggits 3 one

Give me an example of what's not making sense. So that I can understand if its grammatical mistake that's causing the problem or something else.