Kubernetes Overview

Image source: Khtan66 CC BY-SA 4.0, from Wikimedia Commons

• To work with Kubernetes, you use Kubernetes API objects to describe your cluster’s desired state
• You set your desired state by creating objects using the Kubernetes API, typically via the command-line interface, kubectl
• You can also use the Kubernetes API directly to interact with the cluster and set or modify your desired state
• Kubernetes Control Plane works to make the cluster’s current state match the desired state
• Kubernetes performs a variety of tasks automatically
  • such as starting or restarting containers
  • scaling the number of replicas of a given application
  • and a lot more

Kubernetes Master

The Kubernetes Master is a collection of three processes that run on a single node in your cluster, which is designated as the master node. Those processes are

• kube-apiserver
• kube-controller-manager
• kube-scheduler

Kubernetes Node

Each individual non-master node in your cluster runs two processes:

• kubelet, which communicates with the Kubernetes Master
• kube-proxy, a network proxy which reflects Kubernetes networking services on each node

Kubernetes Objects

Kubernetes contains a number of abstractions that represent the state of your system. These abstractions are represented by objects in the Kubernetes API; see the Kubernetes Objects overview for more details.

Basic Objects

The basic Kubernetes objects include:

• Pod
• Service
• Volume
• Namespace

Higher Level Abstractions

In addition, Kubernetes contains a number of higher-level abstractions called Controllers. Controllers build upon the basic objects, and provide additional functionality and convenience features. They include

• ReplicaSet
• Deployment
• StatefulSet
• DaemonSet
• Job