Glossary

Table of Contents

A | B | C | D | E | H | I | K | L| M | N | O | P | R | S | T | W

A


Add-ons

Services beyond the fundamental components of Kubernetes.

  • Core Add-ons: Addons that are required to deploy a Kubernetes-conformant cluster: DNS, kube-proxy, CNI.
  • Additional Add-ons: Addons that are not required for a Kubernetes-conformant cluster (e.g. metrics/Heapster, Dashboard).

B


Bootstrap

The process of turning a server into a Kubernetes node. This may involve assembling data to provide when creating the server that backs the Machine, as well as runtime configuration of the software running on that server.

Bootstrap cluster

A temporary cluster that is used to provision a Target Management cluster.

Bootstrap provider

Refers to a provider that implements a solution for the bootstrap process. Bootstrap provider’s interaction with Cluster API is based on what is defined in the Cluster API contract.

See CABPK.

C


CAEP

Cluster API Enhancement Proposal - patterned after KEP. See template

CAPI

Core Cluster API

CAPA

Cluster API Provider AWS

CABPK

Cluster API Bootstrap Provider Kubeadm

CAPC

Cluster API Provider CloudStack

CAPD

Cluster API Provider Docker

CAPDO

Cluster API Provider DigitalOcean

CAPG

Cluster API Google Cloud Provider

CAPH

Cluster API Provider Hetzner

CAPIBM

Cluster API Provider IBM Cloud

CAPM3

Cluster API Provider Metal3

CAPN

Cluster API Provider Nested

CAPX

Cluster API Provider Nutanix

CAPKK

Cluster API Provider KubeKey

CAPK

Cluster API Provider Kubevirt

CAPO

Cluster API Provider OpenStack

CAPOSC

Cluster API Provider Outscale

CAPOCI

Cluster API Provider Oracle Cloud Infrastructure (OCI)

CAPV

Cluster API Provider vSphere

CAPVC

Cluster API Provider vcluster

CAPVCD

Cluster API Provider VMware Cloud Director

CAPZ

Cluster API Provider Azure

Cloud provider

Or Cloud service provider

Refers to an information technology (IT) company that provides computing resources (e.g. AWS, Azure, Google, etc.).

Cluster

A full Kubernetes deployment. See Management Cluster and Workload Cluster.

ClusterClass

A collection of templates that define a topology (control plane and workers) to be used to continuously reconcile one or more Clusters. See ClusterClass

Cluster API

Or Cluster API project

The Cluster API sub-project of the SIG-cluster-lifecycle. It is also used to refer to the software components, APIs, and community that produce them.

See core provider

Cluster API Runtime

The Cluster API execution model, a set of controllers cooperating in managing the Kubernetes cluster lifecycle.

Contract

Or Cluster API contract

Defines a set of rules a provider is expected to comply with in order to interact with Cluster API. Those rules can be in the form of CustomResourceDefinition (CRD) fields and/or expected behaviors to be implemented.

Control plane

The set of Kubernetes services that form the basis of a cluster. See also https://kubernetes.io/docs/concepts/#kubernetes-control-plane There are two variants:

  • Self-provisioned: A Kubernetes control plane consisting of pods or machines wholly managed by a single Cluster API deployment.
  • External or Managed: A control plane offered and controlled by some system other than Cluster API (e.g., GKE, AKS, EKS, IKS).

Control plane provider

Refers to a provider that implements a solution for the management of a Kubernetes control plane. Control plane provider’s interaction with Cluster API is based on what is defined in the Cluster API contract.

See KCP.

Core provider

Refers to a provider that implements Cluster API core controllers; if you consider that the first project that must be deployed in a management Cluster is Cluster API itself, it should be clear why the Cluster API project is also referred to as the core provider.

See CAPI.

D


Default implementation

A feature implementation offered as part of the Cluster API project and maintained by the CAPI core team; For example KCP is a default implementation for a control plane provider.

E


External patch

Patch generated by an external component using Runtime SDK. Alternative to inline patch.

External patch extension

A runtime extension that implements a topology mutation hook.

H


Horizontal Scaling

The ability to add more machines based on policy and well defined metrics. For example, add a machine to a cluster when CPU load average > (X) for a period of time (Y).

Host

see Server

I


Infrastructure provider

Refers to a provider that implements provisioning of infrastructure/computational resources required by the Cluster or by Machines (e.g. VMs, networking, etc.). Infrastructure provider’s interaction with Cluster API is based on what is defined in the Cluster API contract.

Clouds infrastructure providers include AWS, Azure, or Google; while VMware, MAAS, or metal3.io can be defined as bare metal providers. When there is more than one way to obtain resources from the same infrastructure provider (e.g. EC2 vs. EKS in AWS) each way is referred to as a variant.

For a complete list of providers see Provider Implementations.

Inline patch

A patch defined inline in a ClusterClass. An alternative to an external patch.

In-place mutable fields

Fields which changes would only impact Kubernetes objects or/and controller behaviour but they won’t mutate in any way provider infrastructure nor the software running on it. In-place mutable fields are propagated in place by CAPI controllers to avoid the more elaborated mechanics of a replace rollout. They include metadata, MinReadySeconds, NodeDrainTimeout, NodeVolumeDetachTimeout and NodeDeletionTimeout but are not limited to be expanded in the future.

Instance

see Server

Immutability

A resource that does not mutate. In kubernetes we often state the instance of a running pod is immutable or does not change once it is run. In order to make a change, a new pod is run. In the context of Cluster API we often refer to a running instance of a Machine as being immutable, from a Cluster API perspective.

IPAM provider

Refers to a provider that allows Cluster API to interact with IPAM solutions. IPAM provider’s interaction with Cluster API is based on the IPAddressClaim and IPAddress API types.

K


Kubernetes-conformant

Or Kubernetes-compliant

A cluster that passes the Kubernetes conformance tests.

k/k

Refers to the main Kubernetes git repository or the main Kubernetes project.

KCP

Kubeadm Control plane Provider

L


Lifecycle hook

A Runtime Hook that allows external components to interact with the lifecycle of a Cluster.

See Implementing Lifecycle Hooks

M


Machine

Or Machine Resource

The Custom Resource for Kubernetes that represents a request to have a place to run kubelet.

See also: Server

Manage a cluster

Perform create, scale, upgrade, or destroy operations on the cluster.

Managed Topology

See Topology

Management cluster

The cluster where one or more Infrastructure Providers run, and where resources (e.g. Machines) are stored. Typically referred to when you are provisioning multiple workload clusters.

Multi-tenancy

Multi tenancy in Cluster API defines the capability of an infrastructure provider to manage different credentials, each one of them corresponding to an infrastructure tenant.

Please note that up until v1alpha3 this concept had a different meaning, referring to the capability to run multiple instances of the same provider, each one with its own credentials; starting from v1alpha4 we are disambiguating the two concepts.

See Multi-tenancy and Support multiple instances.

N


Node pools

A node pool is a group of nodes within a cluster that all have the same configuration.

O


Operating system

Or OS

A generically understood combination of a kernel and system-level userspace interface, such as Linux or Windows, as opposed to a particular distribution.

P


Patch

A set of instructions describing modifications to a Kubernetes object. Examples include JSON Patch and JSON Merge Patch.

Pivot

Pivot is a process for moving the provider components and declared cluster-api resources from a Source Management cluster to a Target Management cluster.

The pivot process is also used for deleting a management cluster and could also be used during an upgrade of the management cluster.

Provider

Or Cluster API provider

This term was originally used as abbreviation for Infrastructure provider, but currently it is used to refer to any project that can be deployed and provides functionality to the Cluster API management Cluster.

See Bootstrap provider, Control plane provider, Core provider, Infrastructure provider, IPAM provider Runtime extension provider.

Provider components

Refers to the YAML artifact published as part of the release process for providers; it usually includes Custom Resource Definitions (CRDs), Deployments (to run the controller manager), RBAC, etc.

In some cases, the same expression is used to refer to the instances of above components deployed in a management cluster.

See Provider repository

Provider repository

Refers to the location where the YAML for provider components are hosted; usually a provider repository hosts many version of provider components, one for each released version.

R


Runtime Extension

An external component which is part of a system built on top of Cluster API that can handle requests for a specific Runtime Hook.

See Runtime SDK

Runtime Extension provider

Refers to a provider that implements one or more runtime extensions. Runtime Extension provider’s interaction with Cluster API are based on the Open API spec for runtime hooks.

Runtime Hook

A single, well identified, extension point allowing applications built on top of Cluster API to hook into specific moments of the Cluster API Runtime, e.g. BeforeClusterUpgrade, TopologyMutationHook.

See Runtime SDK

Runtime SDK

A developer toolkit required to build Runtime Hooks and Runtime Extensions.

See Runtime SDK

S


Scaling

Unless otherwise specified, this refers to horizontal scaling.

Stacked control plane

A control plane node where etcd is colocated with the Kubernetes API server, and is running as a static pod.

Server

The infrastructure that backs a Machine Resource, typically either a cloud instance, virtual machine, or physical host.

T


Topology

A field in the Cluster object spec that allows defining and managing the shape of the Cluster’s control plane and worker machines from a single point of control. The Cluster’s topology is based on a ClusterClass. Sometimes it is also referred as a managed topology.

See ClusterClass

Topology Mutation Hook

A Runtime Hook that allows external components to generate patches for customizing Kubernetes objects that are part of a Cluster topology.

See Topology Mutation

W


Workload Cluster

A cluster created by a ClusterAPI controller, which is not a bootstrap cluster, and is meant to be used by end-users, as opposed to by CAPI tooling.

WorkerClass

A collection of templates that define a set of worker nodes in the cluster. A ClusterClass contains zero or more WorkerClass definitions.

See ClusterClass