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Asked: 2024-09-25T01:32:16+05:30 In:

How can I utilize client-go to interact with Kubernetes Custom Resource Definitions (CRDs)?

I’ve been diving into Kubernetes and playing around with Custom Resource Definitions (CRDs) lately. It’s pretty amazing how CRDs let you extend Kubernetes capabilities, but I’ve hit a bit of a wall while trying to figure out how to interact with them using client-go. I know client-go is the official Go client for Kubernetes, and it seems like the right tool for the job, but when it comes to CRDs, things get a bit murky.

So, here’s my situation: I have a custom resource defined for managing some specific application configurations in my cluster. I wrote the CRD and can see it in my Kubernetes API, which feels like a small victory! Now, I want to create, read, update, and delete instances of this custom resource programmatically using client-go. I’ve looked around and found bits and pieces on how to set up client-go, but I’m struggling to piece it all together specifically for CRDs.

What I really need is a step-by-step or at least a solid overview of how to utilize client-go to interact with this CRD. Like, do I need to create a custom clientset, or can I use the generic Kubernetes client? And what about using informers or listers? How do these fit in when you’re working with CRDs? I’ve seen some examples floating around, but they all seem to skip around and assume so much prior knowledge.

If anyone has gone through this process or has any advice on best practices, I’d love to hear your thoughts! Are there particular pitfalls to watch out for? Are there any helpful libraries or resources that could make this process easier? I really want to make this work and get more comfortable with client-go and CRDs, so any tips or examples would be super appreciated!

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    2 Answers



    1. Kubernetes CRD with client-go

      Interacting with CRDs using client-go

      Alright, diving into CRDs with client-go can feel a bit overwhelming at first, but don’t worry! Let’s break it down step by step.

      1. Setting Up Your Client

      First off, you do need a custom clientset for your CRD. If you have a CRD named MyAppConfig, you’ll want to generate a clientset. The easiest way to do this is by using the kubebuilder tool or the controller-gen tool.

      Generate the clientset with:

      make client

      2. Using the Clientset

      After setting up your clientset, you can start using it to create, read, update, or delete your custom resources. Here’s a simple way to do each:

      Create Resource

      myResource, err := clientset.MyappV1().MyAppConfigs(namespace).Create(ctx, &myAppConfig, metav1.CreateOptions{})

      Read Resource

      myResource, err := clientset.MyappV1().MyAppConfigs(namespace).Get(ctx, name, metav1.GetOptions{})

      Update Resource

      myResource, err := clientset.MyappV1().MyAppConfigs(namespace).Update(ctx, updatedMyAppConfig, metav1.UpdateOptions{})

      Delete Resource

      err := clientset.MyappV1().MyAppConfigs(namespace).Delete(ctx, name, metav1.DeleteOptions{})

      3. Informers and Listers

      Informers and listers are super helpful when you want to watch for changes to your CRDs. Instead of repeatedly querying the API server, you can set up an informer to watch for changes and keep a local cache.

      Here’s how you can set up an informer:

      
informer := informers.NewFilteredMyAppConfigInformer(
    kubeClient,
    namespace,
    0, // Resync period
    cache.Indexers{},
    )

      Then you can start it and add event handlers to manage adds, updates, and deletes.

      4. Some Tips

      • Ensure your CRD is registered properly in Kubernetes.
      • Double-check the API version when making calls – small typos can lead to headaches!
      • Make sure your context is set up correctly when using the client.
      • Start with simple objects before moving on to more complex configurations.

      5. Helpful Resources

      Here are some links that might help you:

      With these steps, you should be able to start interacting with your CRD using client-go! Just take it slow, and it’ll click.


    2. Interacting with Custom Resource Definitions (CRDs) using client-go involves a few key steps to effectively manage your custom resources. Firstly, you’ll want to establish a custom clientset for your CRD to enable specific operations such as creating, reading, updating, and deleting instances of the custom resource. Start by defining your CRD in Go, which involves creating Go types that map to your CRD structure. Then, generate the clientset using a tool like the Kubernetes client-go generator. This clientset will offer you type-safe methods to interact with your custom resources, allowing you to avoid the common pitfalls of raw API calls.

      In addition to the clientset, using informers and listers can greatly improve how you manage the lifecycle of your custom resources. Informers watch for changes to the resources and can trigger events that your application can respond to. Listers, on the other hand, provide a more efficient way to list and get these resources without directly querying the API server each time. When setting them up, ensure your informers are initialized correctly and use the clientset you’ve established. For more comprehensive examples and guidance, refer to the official client-go documentation, which contains tutorials on setting up clientsets and using informers efficiently. Community resources like GitHub repositories featuring CRD examples can also be invaluable for practical insights and best practices.

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