Master node provides connection to the Control Plane service, to the user.
The Control Plane is responsible for managing and operating the whole Kubernetes cluster.
Each Control Plane service run with independent role and performs separate operation.
The user interface is usually command line interface, or web dashboard or API.
Master Components
Master node has 4 main components-
WARNING
If the master node is down, then the whole cluster goes down.
That is why one or more replicas of the master node are created in the cluster in high availability(HA) mode.
HA mode keeps all master node replicas synchronized.
API Server
API server receives requests (REST calls) from the client (i.e., kubectl).
After receiving any request, the API server accesses data from the etcd key-value storage(if needed). Then performs the operation.
Then, finally writes the new state to etcd.
etcd
etcd is a key-value repository, where Kubernetes stores data.
Scheduler
Scheduler is responsible for assigning objects to nodes.
Controller
Controller is responsible for anaging the state of the cluster.
Controller manages the deployment object
It monitors the cluster’s current state and the status of running Pods.
When pods go offline, the controller’s job is to maintain the number of running pods.