cdk8s-operator

Create Kubernetes CRD Operators using CDK8s Constructs

This is a multi-language (jsii) library and a command-line tool that allows you to create Kubernetes operators for CRDs (Custom Resource Definitions) using CDK8s.

Getting Started

Let's create our first CRD served by a CDK8s construct using TypeScript.

Install CDK8s

Make sure your system has the required CDK8s prerequisites.

Install the CDK8s CLI globally through npm:

$ npm i -g cdk8s-cli
Installing...

# Verify installation
$ cdk8s --version
1.0.0-beta.3

Create a new CDK8s app

Now, let's create a new CDK8s typescript app:

mkdir hello-operator && cd hello-operator
git init
cdk8s init typescript-app

Install cdk8s-operator

Next, let's install this module as a dependency of our TypeScript project:

npm install cdk8s-operator

Construct

We will start by creating the construct that implements the abstraction. This is is just a normal CDK8s custom construct:

Let's create a construct called PodCollection which represents a collection of pods:

pod-collection.ts:

import { Pod } from 'cdk8s-plus-17';
import { Construct } from 'constructs';

export interface PodCollectionProps {
  /** Number of pods */
  readonly count: number;
  /** The docker image to deploy */
  readonly image: string;
}

export class PodCollection extends Construct {
  constructor(scope: Construct, id: string, props: PodCollectionProps) {
    super(scope, id);

    for (let i = 0; i < props.count; ++i) {
      new Pod(this, `pod-${i}`, {
        containers: [ { image: props.image } ]
      });
    }
  }
}

Operator App

Now, we will need to replace out main.ts file with an "operator app", which is a special kind of CDK8s app designed to be executed by the cdk8s-server CLI which is included in this module.

The Operator app construct can be used to create "CDK8s Operators" which are CDK8s apps that accept input from a file (or STDIN) with a Kubernetes manifest, instantiates a construct with the spec as its input and emits the resulting manifest to STDOUT.

Replace the contents of main.ts with the following. We initialize an Operator app and then register a provider which handles resources of API version samples.cdk8s.org/v1alpha1 and kind PodCollection.

main.ts:

import { Operator } from 'cdk8s-operator';
import { PodCollection } from './pod-collection';

const app = new Operator();

app.addProvider({
  apiVersion: 'samples.cdk8s.org/v1alpha1',
  kind: 'PodCollection',
  handler: {
    apply: (scope, id, props) => new PodCollection(scope, id, props)
  }
})

app.synth();

A single operator can handle any number of resource kinds. Simply call addProvider() for each apiVersion/kind.

Using Operators

To use this operator, create an input.json file, e.g:

input.json:

{
  "apiVersion": "samples.cdk8s.org/v1alpha1",
  "kind": "PodCollection",
  "metadata": {
    "name": "my-collection"
  },
  "spec": {
    "image": "paulbouwer/hello-kubernetes",
    "count": 5
  }
}

Compile your code:

# delete `main.test.ts` since it has some code that won't compile
$ rm -f main.test.*

# compile
$ npm run compile

And run:

$ node main.js input.json

apiVersion: "v1"
kind: "Pod"
metadata:
  name: "my-collection-pod-0-c8735c52"
spec:
  containers:
    - env: []
      image: "paulbouwer/hello-kubernetes"
      imagePullPolicy: "Always"
      name: "main"
      ports: []
      volumeMounts: []
  volumes: []
---
apiVersion: "v1"
kind: "Pod"
metadata:
  name: "my-collection-pod-1-c89f58d7"
spec:
  containers:
    - env: []
      image: "paulbouwer/hello-kubernetes"
      imagePullPolicy: "Always"
      name: "main"
      ports: []
      volumeMounts: []
  volumes: []
---
apiVersion: "v1"
kind: "Pod"
metadata:
  name: "my-collection-pod-2-c88d4268"
spec:
  containers:
    - env: []
      image: "paulbouwer/hello-kubernetes"
      imagePullPolicy: "Always"
      name: "main"
      ports: []
      volumeMounts: []
  volumes: []
---
apiVersion: "v1"
kind: "Pod"
metadata:
  name: "my-collection-pod-3-c86866b1"
spec:
  containers:
    - env: []
      image: "paulbouwer/hello-kubernetes"
      imagePullPolicy: "Always"
      name: "main"
      ports: []
      volumeMounts: []
  volumes: []
---
apiVersion: "v1"
kind: "Pod"
metadata:
  name: "my-collection-pod-4-c8b74b1d"
spec:
  containers:
    - env: []
      image: "paulbouwer/hello-kubernetes"
      imagePullPolicy: "Always"
      name: "main"
      ports: []
      volumeMounts: []
  volumes: []

cdk8s-server

This library is shipped with a program called cdk8s-server which can be used to host your operator inside an HTTP server. This server can be used as a sidecar container with a generic CRD operator (TBD).

$ PORT=8080 npx cdk8s-server
Listening on 8080
- App command: node main.js
- Request body should include a single k8s resource in JSON format
- Request will be piped through STDIN to "node main.js"
- Response is the STDOUT and expected to be a multi-resource yaml manifest

Now, you can send input.json over HTTP:

$ curl -d @input.json http://localhost:8080
MANIFEST...

License

Apache 2.0