Kubernetes is an open-source orchestration platform for automating the deployment, scaling, and management of containerized applications. kubectl is a command-line tool for interacting with a Kubernetes cluster.
While kubectl is extremely powerful, there are times when you might want to add custom functionality to make it even more efficient for your particular workflow. That's where Kubernetes plugins come in.
A Kubernetes plugin is a piece of code that extends the functionality of kubectl. In this article, we'll take a look at how to create a Kubernetes plugin and how to use it to add custom functionality to kubectl.
Kubernetes plugins are written in Go. The plugin code must be compiled into a binary and placed in your PATH. The binary must be named kubectl-{plugin-name}.
The plugin binary must implement the following interface:
type KubernetesPlugin interface {
Run([]string) error
}
The Run() method is called when the plugin is executed and is passed an array of strings containing the plugin's arguments.
Let's take a look at an example plugin that prints a greeting:
package main
import "fmt"
type GreetPlugin struct{}
func (p *GreetPlugin) Run(args []string) error {
fmt.Println("Hello, world!")
return nil
}
func main() {
plugin := &GreetPlugin{}
plugin.Run(nil)
}
To compile the plugin, we can use the go build command:
$ go build -o kubectl-greet ./greet.go
Once the plugin is built, we can add it to our PATH and test it out:
$ export PATH=$PATH:$(pwd)
$ kubectl greet
Hello, world!
Now that we've created a basic Kubernetes plugin, let's look at how we can use it to add custom functionality to kubectl.
For this example, we'll create a plugin that prints a list of the pods in a given namespace. We'll start by defining a struct that contains the information we need to pass to the plugin:
type PodListOptions struct {
Namespace string
}
Next, we'll create a function that parses the plugin's arguments and initializes a PodListOptions struct:
func parseArgs(args []string) (*PodListOptions, error) {
if len(args) == 0 {
return nil, fmt.Errorf("namespace is required")
}
options := &PodListOptions{
Namespace: args[0],
}
return options, nil
}
Now we can update our plugin's Run() method to call our parseArgs() function and use the resulting PodListOptions struct to print a list of the pods in the given namespace:
func (p *PodListPlugin) Run(args []string) error {
options, err := parseArgs(args)
if err != nil {
return err
}
pods, err := p.listPods(options.Namespace)
if err != nil {
return err
}
for _, pod := range pods {
fmt.Println(pod)
}
return nil
}
Finally, we'll need to implement the listPods() method to actually fetch the list of pods from the Kubernetes API:
func (p *PodListPlugin) listPods(namespace string) ([]string, error) {
// TODO: Implement me!
}
With our plugin complete, we can add it to our PATH and test it out:
$ export PATH=$PATH:$(pwd)
$ kubectl pod-list my-namespace
pod-1
pod-2
pod-3
As you can see, Kubernetes plugins provide a great way to add custom functionality to kubectl. With just a few lines of code, you can make kubectl work exactly the way you want it to.
https://kubernetes.io/docs/reference/using-api/extending-api/
https://kubernetes.io/docs/tasks/extend-kubectl/kubectl-plugins/