Abstraction Layers

Software

TODO — High-level abstraction of software modules which make up the LCM.

The YAOOK/K8s life-cycle-management tooling can be abstracted into two main modules: k8s-core and k8s-supplements.

k8s-core

The so-called k8s-core consists of Ansible playbooks which automate and allow the bootstrapping, preparation, configuration and customization of nodes to fulfill the requirements for a high-available Kubernetes cluster as well as the initialization and maintenance of a “vanilla” kubeadm-based Kubernetes cluster.

k8s-supplements

The so-called k8s-supplements consists of Ansible playbooks which complement the very rudimentary Kubernetes cluster initialized by the k8s-core and adds necessary as well as optional but useful surroundings for a fully functional productive Kubernetes environment.

Customization

In order to allow users to use a kind of extensions or additional plays, a drop-in directory is created if enabled which can be used to include custom tasks to the cluster-repository. These plays are automatically executed and are on the top of the abstraction layer as they rely on a working YAOOK/K8s cluster.

The customization layer is enabled by default but can be disabled via an environment variable.

Architecture

Harbour Infrastructure Layer / Undercloud

What we internally call harbor infrastructure layer is generally better known as undercloud and describes the system on which the Kubernetes is deployed. A YAOOK/K8s-cluster can be built upon an already existing OpenStack deployment or directly on bare metal.

In general, network configuration aside, the YAOOK/K8s-LCM requires layer 3 access to a bunch of nodes ideally freshly set up.

YAOOK/K8s on OpenStack

If the Kubernetes cluster runs on top of OpenStack, it has to be connected to the OpenStack layer. On each control plane node, an OpenStack cloud controller manager (CCM) is running that acts as an interface between the cluster and OpenStack. kubelet is started with --cloud-provider=external. Block storage can be dynamically provisioned by OpenStack Cinder via the Cinder Container Storage Interface (CSI) plugin.

YAOOK/K8s on Bare Metal

The Kubernetes cluster can also run directly on bare metal nodes. We differentiate two different scenarios, the bare metal nodes are self-managed or by the yaook/metal-controller is used to provision the nodes and the Kubernetes running on them.

Self-managed Bare Metal

The YAOOK/K8s LCM assumes that you have L3-connectivity to a bunch of nodes. It does not really matter if these are bare metal nodes or VMs on a cloud.

Automated Bare Metal

For further information, please refer to the yaook/metal-controller