k8s-cli-jbang project

This project is an example of how to extend kubernetes cli (kubectl) with a Java application. It demonstrates the use of Kubernetes client-java and access the Kubernetes API. In order to be a kubectl plugin it is necessary to have a file which uses the defined naming convention of kubectl-<plugin-name>. This is a challenge in Java, but can be done with jbang. In order to provide a good CLI experience picocli is used.

This work and demo is provided by Max Andersen creator of j'bang as a followup to a demo of the same using graal. His original work is https://github.com/maxandersen/k8s-cli-java. What a great reminder of how the value the internet can provided!

Prerequisites

• Running Kubernetes 1.15+ cluster. Kind 0.7.0 was used for testing.
• Java 1.8 and jbang 0.16+

j'bang

Why jbang?

The goal of this project is to reduce the experience necessary to integrate a kubectl plugin along with kubernetes interactions in a Java friendly way. This means building an executable or script that is in the path and takes the form of "kubectl-". This can be challenging for a Java application. One approach is to build a native executable image which is possible with graalvm. It was also viewed that the startup time of a Java application would be too slow and native was necessary... than along comes j'bang, providing Java shell scripting. Counter to any performance fears, after the first compilation, it has good startup performance.

j'bang is definitely the fastest feedback loop to experiment with these features.

jbang things to know

• jbang installation
• Make the script kubectl-example in this example executable chmod +x kubectl-example
• The base class must match the script name where the hyphen is ignored and the 2nd word capitalized. So KubectlExample is the class for kubectl-example.

Getting Started

Start a cluster: kind create cluster

and run one of the commands: ./kubectl-exampl pod list

Example:

./kubectl-example pod list
________________________________________________________________
| Pod Name                                  | namespace         |
|===============================================================|
| coredns-6955765f44-f966p                  | kube-system       |
| coredns-6955765f44-xnzbg                  | kube-system       |
| etcd-kind-control-plane                   | kube-system       |
| kindnet-cznll                             | kube-system       |
| kube-apiserver-kind-control-plane         | kube-system       |
| kube-controller-manager-kind-control-plane| kube-system       |
| kube-proxy-tw9cb                          | kube-system       |
| kube-scheduler-kind-control-plane         | kube-system       |
| local-path-provisioner-7745554f7f-gk5j9   | local-path-storage|

List of Commands

• pod list
• pod list2
• pod add [-n namespace] [-i image]
• resources

Adding as a kubectl plugin

The executable needs to be the path. From the root of the project run: export PATH=$PATH:$PWD

Now give kubectl a try with example. run: kubectl example pod list You should get the same output as above.