Extending kubernetes client-go

Question

I'm writing a controller that watches kubernetes service objects, and creates trafficsplits if they contain a certain label.

Since the native kubernetes go client does not support the trafficsplit object, I had to find a way and extend the client so it would recognize the custom resource. I found this guide which was helpful and allowed me to tackle the issue like so -

import (
    "splitClientV1alpha1 "github.com/servicemeshinterface/smi-sdk-go/pkg/gen/client/split/clientset/versioned/typed/split/v1alpha1"
    "k8s.io/client-go/kubernetes"
    ...
)

// getting ./kube/config from file
kubehome := filepath.Join(homedir.HomeDir(), ".kube", "config")
// Building the config from file
kubeConfig, err = clientcmd.BuildConfigFromFlags("", kubehome)
if err != nil {
    return fmt.Errorf("error loading kubernetes configuration: %w", err)
}

// Creating the native client object
kubeClient, err := kubernetes.NewForConfig(kubeConfig)
if err != nil {
    return fmt.Errorf("error creating kubernetes client: %w", err)
}

// Creating another clientset exclusively for the custom resource
splitClient, err := splitClientV1alpha1.NewForConfig(kubeConfig)
if err != nil {
    return fmt.Errorf("error creating split client: %s", err)
}

I feel like there must be a way to extend the kubeClient object with the trafficsplit schema, instead of creating a separate client like I did. Is there any way to achieve this?

Answer 1

This is definitely possible! You want to use go's struct extension features :)

Bsasically, we create a struct that extends both kubernetes.Clientset and splitClientV1alpha1.SplitV1alpha1Client and initialize it using code very similar to yours above. We can then use methods from either client on that struct.

import (
    "fmt"
    splitClientV1alpha1 "github.com/servicemeshinterface/smi-sdk-go/pkg/gen/client/split/clientset/versioned/typed/split/v1alpha1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/clientcmd"
    "k8s.io/client-go/util/homedir"
    "path/filepath"
)

type MyKubeClient struct {
    kubernetes.Clientset
    splitClientV1alpha1.SplitV1alpha1Client
}

func getClient() (*MyKubeClient, error) {
    // getting ./kube/config from file
    kubehome := filepath.Join(homedir.HomeDir(), ".kube", "config")
    // Building the config from file
    kubeConfig, err := clientcmd.BuildConfigFromFlags("", kubehome)
    if err != nil {
        return nil, fmt.Errorf("error loading kubernetes configuration: %w", err)
    }

    // Creating the native client object
    kubeClient, err := kubernetes.NewForConfig(kubeConfig)
    if err != nil {
        return nil, fmt.Errorf("error creating kubernetes client: %w", err)
    }

    // Creating another clientset exclusively for the custom resource
    splitClient, err := splitClientV1alpha1.NewForConfig(kubeConfig)
    if err != nil {
        return nil, fmt.Errorf("error creating split client: %s", err)
    }

    return &MyKubeClient{
        Clientset:           *kubeClient,
        SplitV1alpha1Client: *splitClient,
    }, nil
}

func doSomething() error {
    client, err := getClient()
    if err != nil {
        return err
    }

    client.CoreV1().Pods("").Create(...)
    client.TrafficSplits(...)
}

If you need to pass your custom client to a function that expects only the original kubernetes.ClientSet, you can do that with:

func doSomething() error {
    client, err := getClient()
    if err != nil {
        return err
    }

    useClientSet(&client.Clientset)
}

func useOriginalKubeClientSet(clientSet *kubernetes.Clientset) {
    # ... do things
}