Cluster API and Canonical Kubernetes¶

Cluster API¶

ClusterAPI (CAPI) is an open-source Kubernetes project that provides a declarative API for cluster creation, configuration, and management. It is designed to automate the creation and management of Kubernetes clusters in various environments, including on-premises data centres, public clouds, and edge devices.

CAPI abstracts away the details of infrastructure provisioning, networking, and other low-level tasks, allowing users to define their desired cluster configuration using simple YAML manifests. This makes it easier to create and manage clusters in a repeatable and consistent manner, regardless of the underlying infrastructure. In this way a wide range of infrastructure providers has been made available, including but not limited to MAAS, Amazon Web Services (AWS), Microsoft Azure, Google Cloud Platform (GCP), and OpenStack.

CAPI also abstracts the provisioning and management of Kubernetes clusters allowing for a variety of Kubernetes distributions to be delivered in all of the supported infrastructure providers. Canonical Kubernetes is one such Kubernetes distribution that seamlessly integrates with Cluster API.

Canonical Kubernetes and CAPI¶

With Canonical Kubernetes CAPI you can:

Provision a cluster that meets your needs
- Choose a Canonical Kubernetes version
- Choose the risk level of the track (Kubernetes version) you want to follow - stable, candidate, beta or edge
- Deploy behind proxies
Upgrade clusters with no downtime
- Carry out rolling upgrades for High Availability (HA) clusters and worker nodes
- Carry out in-place upgrades for non-HA control planes and worker nodes

Please refer to the getting started tutorial for a concrete example of a CAPI deployment.

CAPI architecture¶

Being a cloud-native framework, CAPI implements all its components as controllers that run within a Kubernetes cluster.

Infrastructure provider¶

There is a separate controller, called a ‘provider’, for each supported infrastructure substrate. The infrastructure providers are responsible for provisioning physical or virtual nodes and setting up networking elements such as load balancers and virtual networks.

Kubernetes distributions¶

In a similar way, each Kubernetes distribution that integrates with ClusterAPI is managed by either the control plane provider, the bootstrap provider, or both.

Control plane provider: handles the control plane’s specific lifecycle.
Bootstrap provider: responsible for delivering and managing Kubernetes on the nodes.

Management cluster¶

The CAPI providers operate within a Kubernetes cluster known as the management cluster. The administrator is responsible for selecting the desired combination of infrastructure and Kubernetes distribution by instantiating the respective infrastructure, bootstrap, and control plane providers on the management cluster.

The management cluster functions as the control plane for the ClusterAPI operator, which is responsible for provisioning and managing the infrastructure resources necessary for creating and managing additional Kubernetes clusters. It is important to note that the management cluster is not intended to support any other workload, as the workloads are expected to run on the provisioned clusters. As a result, the provisioned clusters are referred to as workload clusters. While CAPI providers mostly live on the management cluster, it’s also possible to maintain the them in the workload cluster. Read more about this in the upstream docs around pivoting.

Canonical Kubernetes providers¶

The Canonical Kubernetes team maintains the two providers required for integrating with CAPI:

Cluster API Bootstrap Provider Canonical Kubernetes¶

The Cluster API Bootstrap Provider Canonical Kubernetes (CABPCK) is responsible for provisioning the nodes in the cluster and preparing them to be joined to the Kubernetes control plane. When you use the CABPCK, you define a Kubernetes Cluster object that describes the desired state of the new cluster. This includes the number and type of nodes in the cluster, as well as any additional configuration settings. The Bootstrap Provider then creates the necessary resources in the Kubernetes API server to bring the cluster up to the desired state. Under the hood, the Bootstrap Provider uses cloud-init to configure the nodes in the cluster. This includes setting up SSH keys, configuring the network, and installing necessary software packages.

Cluster API Control Plane Provider Canonical Kubernetes¶

The Cluster API Control Plane Provider Canonical Kubernetes (CACPCK) enables the creation and management of Kubernetes control planes using Canonical Kubernetes as the underlying Kubernetes distribution. Its main tasks are to update the machine state and to generate the kubeconfig file used for accessing the cluster. The kubeconfig file is stored as a secret which the user can then retrieve using the clusterctl command. This component also handles the upgrade process for the control plane nodes.

Canonical Kubernetes CAPI architecture diagram¶