![]() The API Server runtime is represented by the kube-apiserver binary. The most common operation is to POST a manifest as part of a REST API invocation - once the invocation is authenticated and authorized, the manifest content is validated, then persisted into the cluster store and various controllers kick in to insure that the cluster state matches the desired state expressed in the manifest. All components - internal system components and external user components - communicate exclusively via the API Server and use the same API. The API server is the control plane front-end service. The recommended configuration includes 3 or 5 replicated masters.Ĭontrol Plane System Services API Server kube-apiserver This approach frees up the master nodes' resources to be exclusively used for cluster management activities. ![]() While it is possible to execute user workloads on the master node, this is generally not recommended. Collectively, they represent the control plane. The master nodes are sometimes called heads or head nodes, and most often simply masters or control plane nodes. In production environments, the control plane usually runs across multiple computers, providing fault-tolerance and high availability.Ī master node is a collection of system services that manage the Kubernetes cluster. These components can be run as traditional operating system services (daemons) or as containers. The control plane makes workload scheduling decisions, performs monitoring and responds to external and internal events. The control plane exposes the API via the API Server and contains the cluster store, which stores state in etcd, the controller manager, the cloud controller manager, the scheduler and other management components. The control plane consists of cluster control components that expose APIs and interfaces to define, deploy, and manage the lifecycle of containers. The control plane is the collective name for a cluster's master nodes. Each Kubernetes node runs a standard set of node components: the kubelet, the kube-proxy and the container runtime.Įach node runs an agent called kubelet: kubelet kube-proxyĮach node runs a process called kube-proxy that is involved in establishing a cluster-wide virtual network across nodes: kube-proxy Container Runtime Container Runtime Control Plane The controller manager includes a node controller. In most cases, the term "node" means worker node. ![]() The worker nodes run the cluster's workload and are collectively known as the data plane.Ī node is a Linux host that can run as a VM, a bare-metal device or an instance in a private or public cloud. Kubernetes cluster with zero workers nodes are possible, and had been seen, but they are quite useless. The rest of the nodes, a potentially relatively larger number, but at least one, are the worker nodes. ![]() They are referred to as master nodes, also collectively known as the control plane. Of those, a small number are running applications that manage the cluster. When you deploy Kubernetes, you get a cluster.Ī Kubernetes cluster consists of a set of nodes, which all run containerized applications.
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