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Components

A component is a collection of Kubernetes manifests including all resources needed for an application, such as a Deployment, a Service or a Secret.

Folder Structure​

A component should be placed in components/<name>.js or components/<name>/index.js.

.
└── components
    ├── foo
    │   └── index.js
    └── nginx.js

When you run kosko generate, Kosko will find all files or folders in components folder that matching the pattern set in components configuration (it is * by default, which means everything in components folder). You can add component names or patterns to the command to specify which components to generate.

# Use `components` in `kosko.toml`.
kosko generate

# Specify which components to generate
kosko generate nginx dev_*

Basic​

Let's start with a basic component. In the following example, we will create a new file components/busybox.js that exports a Pod.

import { Pod } from "kubernetes-models/v1/Pod";

const pod = new Pod({
  metadata: { name: "busybox" },
  spec: {
    containers: [{ name: "busybox", image: "busybox" }]
  }
});

export default pod;

Then you can run kosko generate to print YAML.

apiVersion: v1
kind: Pod
metadata:
  name: busybox
spec:
  containers:
    - name: busybox
      image: busybox

At the first line, we import Pod class from kubernetes-models package. This is a separated package which is generated automatically from Kubernetes OpenAPI Specification. It provides type definitions and validation. You can import corresponding resources as below.

// Class
import { Kind } from "kubernetes-models/<apiVersion>/<kind>";

// Interface
import { IKind } from "kubernetes-models/<apiVersion>/<kind>";

Kind can be omitted from the import path if you want to import multiple resources at a time. Please note that this might have impact on the module loading speed.

import { Pod, Service } from "kubernetes-models/v1";

kubernetes-models also supports custom resource definitions (CRDs). You can see here for a full list of supported 3rd-party models.

import { Certificate } from "@kubernetes-models/cert-manager/cert-manager.io/v1/Certificate";

If the CRD package is not available yet, or you want to skip validation on certain manifests, Kosko also supports plain objects.

const pod = {
  apiVersion: "v1",
  kind: "Pod"
};

Export More Manifests​

In the following example, we will create a file components/nginx.js that exports a Deployment and Service.

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

const labels = { app: "nginx" };

const deployment = new Deployment({
  metadata: { name: "nginx" },
  spec: {
    selector: {
      matchLabels: labels
    },
    template: {
      metadata: { labels },
      spec: {
        containers: [{ name: "nginx", image: "nginx" }]
      }
    }
  }
});

const service = new Service({
  metadata: { name: "nginx" },
  spec: {
    selector: labels,
    ports: [{ port: 80 }]
  }
});

export default [deployment, service];

At the last line, we replace the export value with an array. So when you run kosko generate, it will print YAML as below.

---
apiVersion: apps/v1
kind: Deployment
(omitted)
---
apiVersion: v1
kind: Service
(omitted)

Function​

You can also export a function that returns an array of manifests.

export default function () {
  return [new Deployment(), new Service()];
}

Async Function​

export default async function () {
  return [new Deployment(), new Service()];
}

Iterable​

Besides array, objects which implements the iterable protocol, such as Set, Map or generator functions, are also supported.

// Set
export default new Set([new Deployment(), new Service()]);

// Generator function
function* gen() {
  yield new Deployment();
  yield new Service();
}

export default gen();

Async Iterable​

// Async generator function
async function* gen() {
  yield new Deployment();
  yield new Service();
}

export default gen();

Nested Manifests​

Available since
  • kosko v1.0.0

All of the patterns we just mentioned above can be combined together. It is very useful for reusing manifests across components.

For example, we can create a function that returns a database as a resource, and use it later in components.

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

function createDatabase(name: string) {
  const metadata = { name: `${name}-db` };
  return [new Deployment({ metadata }), new Service({ metadata })];
}

export default [
  createDatabase("my-app"),
  new Deployment({ metadata: { name: "my-app" } }),
  new Service({ metadata: { name: "my-app" } })
];

All manifests in arrays and functions will be flattened. Below is YAML output.

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app-db
---
apiVersion: v1
kind: Service
metadata:
  name: my-app-db
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
---
apiVersion: v1
kind: Service
metadata:
  name: my-app