A Kubernetes Cluster consists of a Master and a Node, on which several Kubernetes services run.
Master node
The Master is the brain of the Kubernetes Cluster, running the following Daemon services: kube-apiserver, kube-scheduler, kube-controller-manager, etcd, and pod networking (eg flannel).
API Server （be apiserver）
API Server provides HTTP/HTTPS RESTful API, Kubernetes API. API Server is the front-end interface of Kubernetes Cluster, through which various client tools (CLI or UI) and other components of Kubernetes can manage various resources of Cluster.
Scheduler（kube-scheduler）
The Scheduler is responsible for deciding which Node to run the Pod on. The Scheduler will fully consider the cluster topology, the current load of each node, and the application's requirements for high availability, performance, and data affinity when scheduling.
Controller Manager（kube-controller-manager）
The Controller Manager is responsible for managing various resources of the Cluster and ensuring that the resources are in the expected state. Controller Manager consists of various controllers, including replication controller, endpoints controller, namespace controller, serviceaccounts controller, etc.
Different controllers manage different resources. For example, the replication controller manages the lifecycle of Deployment, StatefulSet, and DaemonSet, and the namespace controller manages Namespace resources.
etcd
etcd is responsible for saving the configuration information of Kubernetes Cluster and the status information of various resources. When data changes, etcd will quickly notify Kubernetes related components.
Pod network
For Pods to be able to communicate with each other, Kubernetes Cluster must deploy a network of Pods, and flannel is one of the options.
These are the components running on the Master, and in the next section we discuss Node.
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