1 개요
- Concepts
- 개념
2 관리 클러스터
워크로드 클러스터의 수명주기를 관리하는 Kubernetes 클러스터. 관리 클러스터는 하나 이상의 제공자가 실행되는 곳이자 머신과 같은 리소스가 저장되는 곳이기도 합니다.
2.1 워크로드 클러스터
관리 클러스터에서 수명주기를 관리하는 Kubernetes 클러스터.
3 인프라 제공자
클러스터 또는 머신(예: VM, 네트워킹 등)에 필요한 인프라/컴퓨팅 리소스의 프로비저닝을 담당하는 구성요소. 예를 들어, 클라우드 인프라 제공자로는 AWS, Azure, Google가 있고 베어메탈 인프라 제공자로는 VMware, MAAS, metal3.io가 있습니다.
같은 인프라 제공자(예: EC2와 EKS를 모두 제공하는 AWS)로부터 리소스를 얻는 방법이 두 가지 이상인 경우, 각 방법을 베리언트(variant)라고 합니다.
4 부트스트랩 제공자
A component responsible for turning a server into a Kubernetes node as well as for:
Generating the cluster certificates, if not otherwise specified Initializing the control plane, and gating the creation of other nodes until it is complete Joining control plane and worker nodes to the cluster
5 컨트롤 플레인
The control plane is a set of components that serve the Kubernetes API and continuously reconcile desired state using control loops.
Self-provisioned: A Kubernetes control plane consisting of pods or machines wholly managed by a single Cluster API deployment. e.g kubeadm uses static pods for running components such as kube-apiserver, kube-controller-manager and kube-scheduler on control plane machines.
Pod-based deployments require an external hosting cluster. The control plane components are deployed using standard Deployment and StatefulSet objects and the API is exposed using a Service.
External or Managed control planes are offered and controlled by some system other than Cluster API, such as GKE, AKS, EKS, or IKS.
The default provider uses kubeadm to bootstrap the control plane. As of v1alpha3, it exposes the configuration via the KubeadmControlPlane object. The controller, capi-kubeadm-control-plane-controller-manager, can then create Machine and BootstrapConfig objects based on the requested replicas in the KubeadmControlPlane object.
6 커스텀 리소스 정의 (CRDs)
A CustomResourceDefinition is a built-in resource that lets you extend the Kubernetes API. Each CustomResourceDefinition represents a customization of a Kubernetes installation. The Cluster API provides and relies on several CustomResourceDefinitions:
6.1 Machine
A “Machine” is the declarative spec for an infrastructure component hosting a Kubernetes Node (for example, a VM). If a new Machine object is created, a provider-specific controller will provision and install a new host to register as a new Node matching the Machine spec. If the Machine’s spec is updated, the controller replaces the host with a new one matching the updated spec. If a Machine object is deleted, its underlying infrastructure and corresponding Node will be deleted by the controller.
Common fields such as Kubernetes version are modeled as fields on the Machine’s spec. Any information that is provider-specific is part of the InfrastructureRef and is not portable between different providers.
6.1.1 Machine Immutability (In-place Upgrade vs. Replace)
From the perspective of Cluster API, all Machines are immutable: once they are created, they are never updated (except for labels, annotations and status), only deleted.
For this reason, MachineDeployments are preferable. MachineDeployments handle changes to machines by replacing them, in the same way core Deployments handle changes to Pod specifications.
6.2 MachineDeployment
A MachineDeployment provides declarative updates for Machines and MachineSets.
A MachineDeployment works similarly to a core Kubernetes Deployment. A MachineDeployment reconciles changes to a Machine spec by rolling out changes to 2 MachineSets, the old and the newly updated.
6.3 MachineSet
A MachineSet’s purpose is to maintain a stable set of Machines running at any given time.
A MachineSet works similarly to a core Kubernetes ReplicaSet. MachineSets are not meant to be used directly, but are the mechanism MachineDeployments use to reconcile desired state.
6.4 MachineHealthCheck
A MachineHealthCheck defines the conditions when a Node should be considered unhealthy.
If the Node matches these unhealthy conditions for a given user-configured time, the MachineHealthCheck initiates remediation of the Node. Remediation of Nodes is performed by deleting the corresponding Machine.
MachineHealthChecks will only remediate Nodes if they are owned by a MachineSet. This ensures that the Kubernetes cluster does not lose capacity, since the MachineSet will create a new Machine to replace the failed Machine.
6.5 BootstrapData
BootstrapData contains the Machine or Node role-specific initialization data (usually cloud-init) used by the Infrastructure Provider to bootstrap a Machine into a Node.
7 참고
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