Klient

Klient is a Simple Kubernetes Client in Go. Its goal is to provide an easy interface to communicate with a Kubernetes cluster similar to using the kubectl commands apply, create, delete and replace.

This package is not a replacement of k8s.io/client-go, its main purpose is to apply, create, delete or replace resources using the YAML or JSON representation of Kubernetes objects. The package k8s.io/client-go requires to know what objects are going to be managed and uses the Kubernetes API to manage them. If you have a file, URL, stream or string with a Kubernetes object to apply (not knowing exactly what's inside) then klient will help you.

This package is part of the blog article Building a Kubernetes Client in Go. Refer to this blog post to know why and how Klient was made.

How to use

Start by importing the package using (import github.com/johandry/klient) and making sure it is in your go.mod file using the latest version executing any go tool command or just go mod tidy. Create the client providing - optionally - the Kubernetes context and the Kubeconfig file location, finally use the methods Apply(), Create(), Delete(), Replace() or it's variations to interact with the Kubernetes cluster.

Example

The following example is to apply a ConfigMap from a []byte variable. It assumes you have a Kubernetes cluster running, accessible and with the Kubeconfig in the default location (~/.kube/config).

It uses klient to apply the ConfigMap and uses the Kubernetes client k8s.io/client-go to get it. This simple example can be done using only k8s.io/client-go to do it all as we know, in advance the object to work with (ConfigMap), however we are dealing with a JSON string representing the ConfigMap, that's why we use klient.

It's unpractical in a real program to apply a resource and then delete it, but just for the purpose of explain how to delete a resource the example deletes the ConfigMap once it's over.

package main

import (
  "log"

  "github.com/johandry/klient"
  metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

func main() {
  name := "apple"
  cm := []byte(`{"apiVersion": "v1", "kind": "ConfigMap", "metadata": { "name": "fruit" }, "data": {	"name": "` + name + `" } }`)

  c := klient.New("", "") // Take the Kubernetes config from the default location (~/.kube/config) and using the default context.
  if err := c.Apply(cm); err != nil {
    log.Fatal("failed to apply the ConfigMap")
  }

  cmFruit, err := c.Clientset.CoreV1().ConfigMaps("default").Get("fruit", metav1.GetOptions{})
  if err != nil {
    log.Fatal("Failed to get the ConfigMap fruits")
  }
  log.Printf("Fruit name: %s", cmFruit.Data["name"])

  if err := c.Delete(cm); err != nil {
    log.Fatal("failed to delete the ConfigMap")
  }
}

For more examples go to the GitHub repository johandry/klient-examples.

Sources and Acknowledge

Many thanks to the contributors of Kubectl and Helm. This package was made inspired by these two amazing projects.

Although it's not so easy or intuitive to use the kubectl code from your Go projects, it's not complex to import and use the Helm Kubernetes client package, so you could either use Klient or the Helm Kubernetes client package to communicate with a Kubernetes cluster.