How can I create a kubernetes.Clientset directly from a GCP service account JSON key file in Go?

Issue

I’m looking for a way to initialise a kubernetes.Clientset for GKE in Go starting from a service account JSON key file. I found a few leads, such as this blog and this associated gist, but the approach outlined there seems to require listing all clusters in a GCP project to create an in-memory representation of the kubeconfig, which isn’t ideal.

Solution

Using the GKE driver code from https://github.com/rancher/kontainer-engine as inspiration, I came up with the following approach (which avoids the dependency on k8s.io/client-go/tools/clientcmd):

package main

import (
    "context"
    "encoding/base64"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
    "strings"

    "golang.org/x/oauth2"
    "golang.org/x/oauth2/google"
    "google.golang.org/api/container/v1"
    "google.golang.org/api/option"
    v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/rest"
)

func getGKEClientset(cluster *container.Cluster, ts oauth2.TokenSource) (kubernetes.Interface, error) {
    capem, err := base64.StdEncoding.DecodeString(cluster.MasterAuth.ClusterCaCertificate)
    if err != nil {
        return nil, fmt.Errorf("failed to decode cluster CA cert: %s", err)
    }

    config := &rest.Config{
        Host: cluster.Endpoint,
        TLSClientConfig: rest.TLSClientConfig{
            CAData: capem,
        },
    }
    config.Wrap(func(rt http.RoundTripper) http.RoundTripper {
        return &oauth2.Transport{
            Source: ts,
            Base:   rt,
        }
    })

    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        return nil, fmt.Errorf("failed to initialise clientset from config: %s", err)
    }

    return clientset, nil
}

func main() {
    gcpServiceAccountKeyFile := "gcp_service_account_key.json"
    gkeLocation := "<GKE Project Location>" // i.e. us-east1
    gkeClusterName := "<GKE Cluster Name>"
    gkeNamespace :=  "<GKE Cluster Namespace>"

    data, err := ioutil.ReadFile(gcpServiceAccountKeyFile)
    if err != nil {
        log.Fatalf("Failed to read GCP service account key file: %s", err)
    }

    ctx := context.Background()

    creds, err := google.CredentialsFromJSON(ctx, data, container.CloudPlatformScope)
    if err != nil {
        log.Fatalf("Failed to load GCP service account credentials: %s", err)
    }

    gkeService, err := container.NewService(ctx, option.WithHTTPClient(oauth2.NewClient(ctx, creds.TokenSource)))
    if err != nil {
        log.Fatalf("Failed to initialise Kubernetes Engine service: %s", err)
    }

    name := fmt.Sprintf("projects/%s/locations/%s/clusters/%s", creds.ProjectID, gkeLocation, gkeClusterName)
    cluster, err := container.NewProjectsLocationsClustersService(gkeService).Get(name).Do()
    if err != nil {
        log.Fatalf("Failed to load GKE cluster %q: %s", name, err)
    }

    clientset, err := getGKEClientset(cluster, creds.TokenSource)
    if err != nil {
        log.Fatalf("Failed to initialise Kubernetes clientset: %s", err)
    }

    pods, err := clientset.CoreV1().Pods(gkeNamespace).List(ctx, v1.ListOptions{})
    if err != nil {
        log.Fatalf("Failed to list pods: %s", err)
    }
    log.Printf("There are %d pods in the namespace", len(pods.Items))
}

Answered By – Mihai Todor

Answer Checked By – Marie Seifert (GoLangFix Admin)

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