Getting started with cdk8s for Typescript¶

In this guide, we’ll walk you through the most essential concepts you need to know in order to build a Kubernetes application using cdk8s for Typescript.

Prerequisites¶

To install the cdk8s CLI, you need the Node Package Manager (npm) installed on your local machine.
cdk8s for Typescript supports Node.js versions 16.20.0+. Check your Node.js version:
```
node --version
```

Set up an environment¶

Install the CLI¶

To initialize a cdk8s project and auto-generate Kubernetes manifests based on our code, we need the cdk8s CLI:

Run the following command to install the CLI using npm. For more installation methods, see Install the cdk8s CLI.
```
npm install -g cdk8s-cli
```

Create a project¶

Next, we’ll initialize a project to create the directory structure and install the necessary dependencies using the init command.

In a terminal window, run the following command in an empty directory:
```
cdk8s init typescript-app
```

In your preferred code editor, open the main.ts file.

import { Construct } from 'constructs';
import { App, Chart, ChartProps } from 'cdk8s';

export class MyChart extends Chart {
  constructor(scope: Construct, id: string, props: ChartProps = { }) {
    super(scope, id, props);

    // define resources here

  }
}

const app = new App();
new MyChart(app, 'typescript');
app.synth();

This sample shows the basic structure of a cdk8s application with the essential libraries: constructs and cdk8s. These libraries supply the foundational classes and methods required for working with cdk8s. It includes the following components:

A custom MyChart class inherits from the Chart base class provided by the cdk8s library, serving as a representation of the Kubernetes resources to be generated and managed.
The constructor method within the MyChart class is responsible for initializing the base class (Chart) and specifying the Kubernetes resources. This method is invoked when creating an instance of the class.
An instance of the App class signifies the primary entry point of the cdk8s application and oversees the application’s lifecycle and resources.
An instance of the MyChart class is created by passing the app instance and a string identifier, “typescript”, as arguments. This action generates and registers the Kubernetes resources defined in the MyChart class within the application. Note that in this example, the “typescript” string identifier is autogenerated based on the current directory name.
The synth method is called on the app instance, which produces the required Kubernetes YAML manifest files based on the defined resources. Note that in this example, we haven’t defined any resources within the MyChart constructor, so running the “cdk8s synth” command in the CLI would generate a blank Kubernetes manifest.

Define Kubernetes resources¶

Now, let’s delve into defining Kubernetes resources for our application. In this example, we’ll outline a basic Kubernetes Deployment for a sample app. We’ll start by importing the imports directory and the k8s sub-directory, which houses the index.ts file containing all cdk8s Kubernetes classes and functions.

Copy the code sample¶

Copy and paste the following code sample into the existing main.ts file of your project.

import { Construct } from 'constructs';
import { App, Chart } from 'cdk8s';
import { KubeDeployment } from './imports/k8s';

class MyChart extends Chart {
  constructor(scope: Construct, ns: string, appLabel: string) {
    super(scope, ns);

    // Define a Kubernetes Deployment
    new KubeDeployment(this, 'my-deployment', {
      spec: {
        replicas: 3,
        selector: { matchLabels: { app: appLabel } },
        template: {
          metadata: { labels: { app: appLabel } },
          spec: {
            containers: [
              {
                name: 'app-container',
                image: 'nginx:1.19.10',
                ports: [{ containerPort: 80 }]
              }
            ]
          }
        }
      }
    });
  }
}

const app = new App();
new MyChart(app, 'getting-started', 'my-app');

app.synth();

A few things worth noting about this sample:

The constructor method in the custom MyChart class employs TypeScript’s type system to construct a Kubernetes Deployment. This Deployment is configured with specific parameters, such as replica count, label selectors, and pod specifications. This approach leverages TypeScript’s type system to dynamically assign the “app” key in label selectors and metadata labels, creating a clear and concise way to set key configuration details.

Generate Kubernetes manifests¶

After you have defined the Kubernetes resources for your application, you are ready to generate the Kubernetes manifest that will define your Deployment resource.

Run the synth command¶

Open a terminal and navigate to your project directory.
Run the synth command. This command generates a Kubernetes manifest file in the dist folder of your project directory. The manifest file contains all the resources you defined inside the MyChart class.
```
cdk8s synth
```

View the manifest¶

Open the dist/getting-started.k8s.yaml file. You should see a Kubernetes manifest similar to the following:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: getting-started-my-deployment-c85252a6
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
        - image: nginx:1.19.10
          name: app-container
          ports:
            - containerPort: 80

Conclusion¶

Throughout this guide, we introduced you to the cdk8s Typescript library and guided you through the process of creating a cdk8s Typescript application. We’ve initiated a simple project and crafted a Kubernetes Deployment using cdk8s code. This involved utilizing TypeScript’s strong type system to dynamically set the “app” key in label selectors and metadata labels for Kubernetes resources.

Next up¶

To run a complete code sample, we recommend diving into the Kubernetes Deployment and Service using the cdk8s-core sample application.