Kubernetes is an open-source system for automating the deployment, scaling, and management of containerized applications. It groups containers that make up an application into logical units called pods. Pods can be scaled up or down to meet the needs of the application. Kubernetes also provides services that allow pods to discover and communicate with each other.
The core components of Kubernetes can be broadly divided into two categories:
Control plane: The control plane is responsible for managing the cluster as a whole. It consists of several components, including:
etcd: A distributed key-value store that stores the cluster state.
API server: The API server is the main point of entry for all Kubernetes operations. It accepts requests from users and other components and performs the necessary actions.
scheduler: The scheduler is responsible for assigning pods to nodes in the cluster.
controller manager: The controller manager runs a number of controllers that manage different aspects of the cluster, such as deployments, replicasets, and services.
Node components: Node components run on each node in the cluster. They are responsible for running pods and communicating with the control plane. The main node components are:
kubelet: The kubelet is the agent that runs on each node. It is responsible for managing pods on the node, including starting, stopping, and restarting them.
container runtime: The container runtime is responsible for running containers on the node. Kubernetes supports multiple container runtimes, such as Docker and containerd.
kube-proxy: The kube-proxy is responsible for implementing network services on the node. It ensures that pods can communicate with each other and with the outside world.
In addition to the core components, Kubernetes also supports a number of optional extensions. These extensions can provide additional functionality, such as logging, monitoring, and a web-based administration interface.