CDK8S DEMO

Introduction

• cdk8s is developed by AWS
• cdk8s are like library, which synthesizes your code into k8s manifests

• cdk8s cli is workflow tool
• cdk8s supports typescript, python, golang

Typescript

This demo will use Typescript.

Overview

1. Run npm install -g cdk8s-cli to install its cli globally.

2. Run cdk8s init typescript-app to create a new typescript cdk8s project.

   • You can see that in package.json and node_modules/, it already has cdk8s dependencies defined and installed. package.json :
   
   • You can also see a cdk8s.yaml generated. And app represents what cdk8s synth command will run (i.e. in this case, cdk8s synth = node main.js). cdk8s.yaml :
   

3. Start your code in main.ts, then compile it to main.js with npm run compile . (This part will have more detail in next section.)

4. Run cdk8s synth to synthesize your code into manifests.

   • K8S manifests will be generated in dist/ folder

Code

• You can make use of npm run watch command. It helps while you are coding, it will automatically compile your .ts to .js on every Save.

• Frequently used class is Chart

  // main.ts
  // for example like this
  // ...
  export class MyChart extends Chart {
    constructor(scope: Construct, id: string, props: ChartProps = { }) {
      super(scope, id, props);
      // define resources here
    }
  }
  // ...

• Easy to create deployment and expose as a service by simply compiling the ts file then run cdk8s synth

  // main.ts
  // ...
  export class MyChart extends Chart {
    constructor(scope: Construct, id: string, props: ChartProps = { }) {
      super(scope, id, props);
      
      const deployment = new kplus.Deployment(this, "nginx", {
      	containers: [{imsage: "nginx"}],  
      }); // cdk8s will synthesize it into a 'Deployment' manifest
      
      deployment.expose(80); // cdk8s will synthesize it into 'Service' manifest
    }
  }
  // ...

• Easy to refactor code for deplicated actions such as deployments, services, so on.

• Use Jest to implement unit tests comparing synthesized result and Chart. This helps detect any expected and unexpected changes. (It is good to include this step in CI pipeline too)

Integration of cdk8s with CI/CD

Imagine a Git repository with a single YAML file that contains a basic Kubernetes manifest (e.g. Deployment + Service). Flux will take care of applying this to your cluster. If you push more changes into this repository Flux will take care of keeping your cluster in the desired state.

• Git branch merge will trigger ci pipeline which eventually synthesize any changes in cdk8s/
• We could design each cluster to pulls from only which branch and which directory path