README.md

Templating Kubernetes resources with Javascript

In this section you will learn how to use Javascript to:

• create JSON (and YAML) definition for a Kubernetes Pod
• submit a Pod definition to the cluster with code

Let's get started.

Prerequisites

Make sure you install all the dependencies with:

npm install

Generating Pod definitions

The code is short:

const { Pod, Container } = require('kubernetes-models/v1')

function createPod(environment = 'production') {
  return new Pod({
    metadata: {
      name: 'test-pod',
    },
    spec: {
      containers: [
        new Container({
          name: 'test-container',
          image: 'k8s.gcr.io/busybox',
          env: [{ name: 'ENV', value: environment }],
        }),
      ],
    },
  })
}

const pod = createPod('dev')

// Any valid JSON is also valid YAML
const json = JSON.stringify(pod, null, 2)

console.log(json)

You can execute the gen-yaml.js script with:

node gen-yaml.js

The output is a JSON object for the Pod.

{
  "metadata": {
    "name": "test-pod"
  },
  "spec": {
    "containers": [
      {
        "name": "test-container",
        "image": "k8s.gcr.io/busybox",
        "env": [
          {
            "name": "ENV",
            "value": "dev"
          }
        ]
      }
    ]
  },
  "apiVersion": "v1",
  "kind": "Pod"
}

But isn't Kubernetes accepting only YAML?

YAML is a superset of JSON and any JSON file is also a valid YAML file.

You can create the Pod in the cluster with the following commands:

node gen-yaml.js > pod.yaml
kubectl apply -f pod.yaml

Creating a custom Kubectl

Instead of exporting the JSON and feeding it to kubectl, you can send the payload to the cluster directly.

You can use the official Kubernetes client library to send the Pod definition to the cluster.

Here's the code:

const { Pod, Container } = require('kubernetes-models/v1')
const k8s = require('@kubernetes/client-node')
const kc = new k8s.KubeConfig()

// Using the default credentials for kubectl
kc.loadFromDefault()
const k8sApi = kc.makeApiClient(k8s.CoreV1Api)

function createPod(environment = 'production') {
  /* return pod definition */
}

const pod = createPod('dev')

k8sApi.createNamespacedPod('default', pod).then(() => console.log('success'))

Assuming you are connected to a running cluster, you can execute the script with:

node kubectl.js

And you can verify that the Pod was created with:

kubectl get pods

What's next

As you can imagine, this is a short demo and you can build more complex objects and use the power of Javascript to compose large objects from smaller ones.