Kubernetes Integration

With the help of the Gardener project, metal-stack can be used for spinning up Kubernetes clusters quickly and reliably on bare metal machines.

To make this happen, we implemented a couple of components, which are described here.


CCM stands for cloud-controller-manager and is the bridge between Kubernetes and a cloud-provider.

We implemented the cloud provider interface in the metal-ccm repository. With the help of the cloud-controller-controller we provide metal-stack-specific properties for Kubernetes clusters, e.g. load balancer configuration through MetalLB or node properties.


To make the firewalls created with metal-stack easily configurable through Kubernetes resources, we add our firewall-controller to the firewall image. The controller watches special CRDs, enabling users to manage:

  • nftables rules
  • Intrusion-detection with suricata
  • network metric collection

Please check out the guide on how to use it.

Gardener components

There are some Gardener resources that need be reconciled when you act as a cloud provider for the Gardener. This section briefly describes the controllers implemented for deploying Kubernetes clusters through Gardener.

If you want to learn how to deploy metal-stack with Gardener, please check out the installation section.


The gardener-extension-provider-metal contains of a set of webhooks and controllers for reconciling or mutating Gardener-specific resources.

The project also contains a validator for metal-type Gardener resources, which you should also deploy in case you want to use metal-stack in combination with Gardener.


Due to the reason we use ignition in our operating system images for userdata, we had to provide an own extension controller for metal-stack, which you can find at Github in the os-metal-extension repository.


Worker nodes are managed through Gardener's machine-controller-manager (MCM). The MCM allows out-of-tree provider implementation via sidecar, which is what we implemented in the machine-controller-manager-provider-metal repository.