Control Plane

The Control Plane decides what happens in the clusters. It doesn’t usually run the application directly, but it manages the entire environment.

Basic Kubernetes Architecture

flowchart LR

    subgraph CP["Control Plane - Node"]
        direction TB

        ETCD[("etcd<br/>Estado do cluster")]
        API["kube-apiserver"]
        SCHED["kube-scheduler"]
        CM["kube-controller-manager"]

        API <--> ETCD
        SCHED <--> API
        CM <--> API
    end

    subgraph W1["Worker Node"]
        direction TB

        KUBELET["kubelet"]
        PROXY["kube-proxy"]
    end

    API <--> KUBELET

etcd

It stores all information. The entire actual state of the cluster. It only communicates with the kube API SERVER.

kube API SERVER

Only it has default permission to communicate with etcd. Its function is to get the status of the cluster as a whole. It’s the one that will communicate with everyone. All cluster communication happens through the kube API SERVER.

kube scheduler

It is responsible for managing where each of the containers will run; it is the controller responsible for placing new containers and knowing the capacity of the nodes.

kube controller manager

It’s the manager of all controllers; it ensures the state of the cluster. It is the cluster’s controller.

Workers

kubelet

It is the Kubernetes agent within the node, and any Kubernetes node will have a kubelet. It’s the one that checks if everything is okay and communicates with the kube APISERVER, receiving the Pod specifications for that node and reporting the state back.

kube proxy

Every node will have a kube proxy. It facilitates communication between pods and the rest of the world, observes cluster resources, and configures network rules on the node.

Ports Used by Kubernetes Components

Component	Default Port	Protocol
kube-apiserver	6443	TCP
etcd	2379–2380	TCP
kube-scheduler	10259	TCP
kube-controller-manager	10257	TCP
kubelet	10250	TCP
kube-proxy	10256	TCP

Application Exposure Ports

Resource	Default Port	Protocol
Service do tipo NodePort	30000–32767	TCP ou UDP

References

Kubernetes — Kubernetes Components — documents the components of the control plane and nodes.
Kubernetes — Ports and Protocols — lists the default ports used by the cluster.
LINUXtips — Kubernetes Essentials — course used as the basis for my studies and these notes.