Kosko: Organizing Kubernetes Manifests with TypeScript

Kosko is a powerful tool that helps you manage Kubernetes manifests using TypeScript. This tutorial will guide you through the main features of Kosko, including organizing manifests, managing multiple environments, ensuring type safety, and identifying issues in your manifests.

1. What is Kosko?

Kosko is a framework that allows you to write Kubernetes manifests using TypeScript. It provides several advantages over traditional YAML-based manifest management:

Type Safety: Leverage TypeScript's static typing to catch errors early.

Code Reusability: Use functions and modules to reduce duplication.

Environment Management: Easily manage configurations for different environments.

Validation: Validate your manifests against Kubernetes OpenAPI schemas.

2. Setting Up Kosko

To get started with Kosko, follow these steps:

1. Install Kosko globally:

 npm install -g kosko        

2. Create a new Kosko project:

mkdir my-k8s-project
cd my-k8s-project
npm create kosko@latest ./        

3. Install necessary dependencies (if not installed automatically during project initialization):

 npm install @kosko/env kosko kubernetes-models        

3. Organizing Kubernetes Manifests

Kosko allows you to organize your manifests into separate TypeScript files. Here's an example structure:

my-k8s-project/
├── components/
│   ├── nginx.ts
├── environments/
│   ├── dev 
│        ├── index.ts
├── package.json
└── kosko.toml        

Example components/nginx.ts:

 import { Deployment } from "kubernetes-models/apps/v1/Deployment";
import { Service } from "kubernetes-models/v1/Service";
import env from "@kosko/env";

const params = env.component("nginx");

const name = "nginx";
const labels = { app: name };
const port = 80;

const deployment = new Deployment({
  metadata: {
    name,
    namespace: params.namespace
  },
  spec: {
    replicas: params.replicas,
    selector: {
      matchLabels: labels
    },
    template: {
      metadata: { labels },
      spec: {
        containers: [
          {
            name: "nginx",
            image: "nginx:stable",
            ports: [{ containerPort: port }],
            env: [{ name: "NGINX_PORT", value: `${port}` }]
          }
        ]
      }
    }
  }
});

const service = new Service({
  metadata: {
    name,
    namespace: params.namespace
  },
  spec: {
    selector: labels,
    ports: [{ port }]
  }
});

export default [deployment, service];        

4. Managing Multiple Environments

Kosko makes it easy to manage different configurations for various environments. Create environment-specific files in the environments folder:

environments/index.ts:

 import { GlobalEnvironment } from "@kosko/env";

const env: GlobalEnvironment = {
  namespace: "dev"
};

export default env;        

To generate manifests for a specific environment:

 kosko generate --env dev        

5. Ensuring Type Safety with OpenAPI Schema

Kosko leverages TypeScript and Kubernetes OpenAPI schemas to provide type safety. Install the necessary packages:

npm install @kubernetes-models/apimachinery @kubernetes-models/base        

Now you can use typed Kubernetes resources:

 const deployment = new Deployment({
  metadata: { name: "example" },
  spec: {          // TypeScript will catch errors like this:
    replicas: "3", // Error: Type 'string' is not assignable to type 'number | undefined'.
    selector: { matchLabels: { app: "example" } },
    template: {
      metadata: { labels: { app: "example" } },
      spec: {
        containers: [
          { name: "example", image: "nginx:latest" }
        ]
      }
    }
  }
});        

6. Finding Issues in Manifests

Kosko provides a validation feature to catch issues in your manifests:

kosko validate --env dev         

This command will check your manifests against the Kubernetes OpenAPI schema and report any issues it finds.

Conclusion

Kosko offers a powerful way to manage Kubernetes manifests using TypeScript. By leveraging type safety, code reusability, and built-in validation, you can create more maintainable and error-free Kubernetes configurations. As you continue to work with Kosko, explore its documentation for more advanced features and best practices.