1

Creating a Go Kubernetes client with client-go

3 years ago

source link: https://dev.to/muaazsaleem/creating-a-go-kubernetes-client-with-client-go-jlf
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.

I mostly use client-go to talk to the Kubernetes API in my go applications.

Whenever I'm starting a new project I inevitably have to figure out the setup steps. I thought I'll just document these for myself here.

A `client-go` "Hello, World!"

Creating a client that implements kubernetes.Interface is just kubernetes.NewForConfig()

import "k8s.io/client-go/kubernetes"

client, err := kubernetes.NewForConfig(kubeconfig)
if err != nil {
    return nil, fmt.Errorf("unable to create a client: %v", err)
}

Enter fullscreen modeExit fullscreen mode

Creating Client Config

Creating the config defers for go clients within and outside of the clients. I think this is mostly because access tokens need to be read to from a mounted file rather than the kubeconfig file.

Creating out of cluster config

import "k8s.io/client-go/tools/clientcmd"

config, err := clientcmd.BuildConfigFromFlags(
    "", kubeconfigPath,
)
if err != nil {
    return nil, fmt.Errorf(
        "unable to load kubeconfig from %s: %v", 
        kubeconfigPath, err,
        )
}

Enter fullscreen modeExit fullscreen mode

Creating in cluster config

import "k8s.io/client-go/rest"

config, err := rest.InClusterConfig()
if err != nil {
    return nil, fmt.Errorf("unable to load in-cluster config: %v", err)
}

Enter fullscreen modeExit fullscreen mode

Putting it all together

import (
    "fmt"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/rest"
    "k8s.io/client-go/tools/clientcmd"
)

func createClient(kubeconfigPath string) (kubernetes.Interface, error) {
    var kubeconfig *rest.Config

    if kubeconfigPath != "" {
        config, err := clientcmd.BuildConfigFromFlags("", kubeconfigPath)
        if err != nil {
            return nil, fmt.Errorf("unable to load kubeconfig from %s: %v", kubeconfigPath, err)
        }
        kubeconfig = config
    } else {
        config, err := rest.InClusterConfig()
        if err != nil {
            return nil, fmt.Errorf("unable to load in-cluster config: %v", err)
        }
        kubeconfig = config
    }

    client, err := kubernetes.NewForConfig(kubeconfig)
    if err != nil {
        return nil, fmt.Errorf("unable to create a client: %v", err)
    }

    return client, nil
}

Enter fullscreen modeExit fullscreen mode

Testing with Fake Client

When testing client-go code it's useful to use the built-in fake client. Here's a short example:

import (
    "context"
    "testing"

    "k8s.io/client-go/kubernetes/fake"
    appsv1 "k8s.io/api/apps/v1"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "github.com/stretchr/testify/require"
)

func TestKubeClient(t *testing.T) {
    fc := fake.NewSimpleClientset(&exampleDeploy)

    deploy, err := fc.AppsV1().Deployments("ns").Get(
        context.Background(),
        "deployment",
        metav1.GetOptions{},
    )

    require.NoError(t, err)

Enter fullscreen modeExit fullscreen mode

Managing package dependencies

client-go version needs to match that of the cluster we're using. I have sometimes had trouble with importing the right k8s.io/api and k8s.io/apimachinery dependencies so here's a example for that as well.

go.mod


module github.com/muaazsaleem/example

go 1.13

require (
// we only really need client-go here the right `api` and 
// `apimachinery` versions "should" get picked up
    k8s.io/client-go v0.19.0
    k8s.io/api v0.19.0
    k8s.io/apimachinery v0.19.0
// stuff I use in pretty much all my projects
    github.com/sirupsen/logrus v1.7.0
    github.com/stretchr/testify v1.6.1
)

Enter fullscreen modeExit fullscreen mode

Further Resources

If you'd like to learn more about building things with the Kubernetes API, Vladimir Vivien has a whole series on it.

The client-go docs have also improved. There are examples now!

Recommend

About Joyk

Aggregate valuable and interesting links.
Joyk means Joy of geeK