cluster-addons.md

Developing addons for hetzner-kube

As of 0.3 adding cluster addons is quite easy, and can happen without altering the core code. You only need to implement the ClusterAddon interface and provide a ClusterAddonInitializer to register your addon to hetzner-kube.

Step 1: Implement the ClusterAddon interface

A cluster interface is described by the following interface:

type ClusterAddon interface {
	Name() string
	Description() string
	URL() string
	Install(args ...string)
	Uninstall()
}

To implement an addon which installs a simple nginx deployment, the addon should be configured like this:

type NginxAddon struct {
	masterNode   *clustermanager.Node
	communicator clustermanager.NodeCommunicator
}

func NewNginxAddon(provider clustermanager.ClusterProvider, communicator clustermanager.NodeCommunicator) ClusterAddon {
	masterNode, err := provider.GetMasterNode()
	FatalOnError(err)
	return &NginxAddon{masterNode: masterNode, communicator: communicator}
}

func (addon *NginxAddon) Name() string {
	return "nginx"
}

func (addon *NginxAddon) Requires() []string {
	return []string{}
}

func (addon *NginxAddon) Description() string {
	return "a simple nginx deployment"
}

func (addon *NginxAddon) URL() string {
	return ""
}

func (addon *NginxAddon) Install(args ...string) {
	node := *addon.masterNode
	_, err := addon.communicator.RunCmd(node, "kubectl run nginx --image nginx")
	FatalOnError(err)
	log.Println("nginx installed")
}

func (addon *NginxAddon) Uninstall() {
	node := *addon.masterNode
	_, err := addon.communicator.RunCmd(node, "kubectl delete deployment nginx")
	FatalOnError(err)
	log.Println("nginx uninstalled")
}

The type should have a field with the pointer to the master node (for running kubectl or helm) and a node communicator (most commonly a SSH client) to run commands. In NewNginxAddon an ClusterProvider and NodeCommunicator instances are injected so you can use them for getting the master node. You can use different data given by provider and define a different type for your addon with custom fields, as long the type still implements ClusterAddon.

Step 2: Register your addon

In the same file you add these lines:

func init() {
	addAddon(NewNginxAddon)
}

addAddon expects a ClusterAddonInitializer, which is a function with a provider and node communicator as parameter and returning a ClusterAddon instance, which is satisfied by NewNginxAddon.

Test

If all done right, you should see now your addon by doing ./hetzner-kube cluster addon list