How to create a Plugin

This section will walk you through a basic plugin development.

Types

If you are using Typescript for developing the plugin, the @kinvolk/headlamp-plugin package does ship some type declarations in @kinvolk/headlamp-plugin/types. Please notice that the whole external plugin mechanics are still in an early development phase and thus only the actual type declarations (and not the corresponding code) is shipped in this package at the moment.

import { Headlamp, Plugin, Registry } from '@kinvolk/headlamp-plugin/lib';

Plugin Class

Plugins are classes that register actions when they are initialized.

A plugin class needs an initialize method which receives a register class that offers ways to register different types of actions in the web UI.

Besides declaring the plugin, an instance of it needs to be registered using the Headlamp.registerPlugin method.

The following example will show a basic plugin declaration and registration in a file that should match the src/index.tsx structure explained in the building section.

import { Headlamp, Plugin, Registry } from '@kinvolk/headlamp-plugin/lib';

class MyPlugin extends Plugin {
  initialize(registry: Registry) {
    console.log('my-plugin initialized');

    // Register your plugin methods here, like:
    // registry.registerSidebarItem(...);
    // registry.registerRoute(...);

    registry.registerAppBarAction('my-plugin-hello', () => <span>Hello</span>);

    return true;
  }
}

Headlamp.registerPlugin('my-plugin', new MyPlugin());

Plugin Example

Let’s create a plugin that just gets the number of pods in the cluster and displays that information in the top bar (i.e. registers an “app bar action”).

import { Headlamp, Plugin, Registry } from '@kinvolk/headlamp-plugin/lib';
import { Typography } from '@material-ui/core';

// import { SectionBox } from '@kinvolk/headlamp-plugin/lib/CommonComponents';
// import { K8s } from '@kinvolk/headlamp-plugin/lib/K8s';

function PodCounter() {
  const [pods, error] = K8s.Pod.useList();
  const msg = pods === null ? 'Loading…' : pods.length.toString();

  return (
      <Typography color="textPrimary">{!error ? `# Pods: ${msg}` : 'Uh, pods!?'}</Typography>
  );
}

class PodCounterPlugin extends Plugin {
  initialize(registry: Registry) {
    registry.registerAppBarAction('pod-counter-action', () =>
      <PodCounter />
    );

    return true;
  }
}

Headlamp.registerPlugin('pod-counter', new PodCounterPlugin());

Here is the result, running Headlamp with this plugin and using with a Minikube cluster:

Please refer to the functionality section for learning about the different functionality that is available to plugins by the registry.