abstraction

Abstraction with KCL

Prerequisite

• Firstly, download and install KCL according to the instructions, and then prepare a Kubernetes environment.

Quick Start

1. Show Config

We can run the following command to show the config.

cat main.k

The output is

import .app

app.App {
    name = "app"
    containers.nginx = {
        image = "nginx"
        ports = [{containerPort = 80}]
    }
    service.ports = [{ port = 80 }]
}

In the above code, we defined a configuration using the App schema, where we configured an nginx container and configured it with an 80 service port.

Besides, KCL allows developers to define the resources required for their applications in a declarative manner and is tied to a platform such as Docker Compose or Kubernetes manifests and allows to generate a platform-specific configuration file such as docker-compose.yaml or a Kubernetes manifests.yaml file. Next, let's generate the corresponding configuration.

2. Transform the Application Config into Docker Compose Config

If we want to transform the application config into the docker compose config, we can run the command simply:

kcl main.k docker_compose_render.k

The output is

services:
  app:
    image: nginx
    ports:
      - published: 80
        target: 80
        protocol: TCP

3. Transform the Application Config into Kubernetes Deployment and Service Manifests

If we want to transform the application config into the Kubernetes manifests, we can run the command simply:

kcl main.k kubernetes_render.k

The output is

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
  labels:
    app: app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: app
  template:
    metadata:
      labels:
        app: app
    spec:
      containers:
        - name: nginx
          image: nginx
          ports:
            - protocol: TCP
              containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: app
  labels:
    app: app
spec:
  selector:
    app: app
  ports:
    - port: 80
      protocol: TCP