Terminology

Mostly taken from the Kubernetes glossary with added changes to help me understand better

• Cluster - A set of machines, called nodes, that run containerized applications managed by Kubernetes. A cluster has at least one worker node and at least one master node.

• Container - A lightweight and portable executable image that contains software and all of its dependencies.

• Container Runtime - The container runtime is the software that is responsible for running containers.

• Container runtime interface (CRI) - The container runtime interface (CRI) is an API for container runtimes to integrate with kubelet on a node.

• Control Plane - The container orchestration layer that exposes the API and interfaces to define, deploy, and manage the lifecycle of containers.

• Controller - In Kubernetes, controllers are control loops that watch the state of your cluster, then make or request changes where needed. Each controller tries to move the current cluster state closer to the desired state.

• DaemonSet - Ensures a copy of a Pod is running across a set of nodes in a cluster.

• Deployment - An API object that manages a replicated application.

• Ephemeral Container - A Container type that you can temporarily run inside a Pod.

• Image - Stored instance of a container that holds a set of software needed to run an application.

• Init Container - One or more initialization containers that must run to completion before any app containers run.

• Job - A finite or batch task that runs to completion.

• kube-controller-manager Component on the master that runs controllers.

• kube-proxy - kube-proxy is a network proxy that runs on each node in your cluster, implementing part of the Kubernetes Service concept.

• Kubectl - A command line tool for communicating with a Kubernetes API server.

• Kubelet An agent that runs on each node in the cluster. It makes sure that containers are running in a pod. Each node must have a Kubelet.

• Kubernetes API - The application that serves Kubernetes functionality through a RESTful interface and stores the state of the cluster.

• Label - Tags objects with identifying attributes that are meaningful and relevant to users (e.g. "environment" : "production").

• Namespace - An abstraction used by Kubernetes to support multiple virtual clusters on the same physical cluster.

• Node - A node is a worker machine in Kubernetes. A node has Pods running inside it.

• NodePort - A service type used to expose the Service on each Node’s IP at a static port (the NodePort). A ClusterIP Service, to which the NodePort Service routes, is automatically created. You’ll be able to contact the NodePort Service, from outside the cluster, by requesting <NodeIP>:<NodePort>.

• Pod - The smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. An example of a pod is a Rails app backend, it can scale up/down horizontally through ReplicaSets which replicates pods.

• ReplicaSet - A ReplicaSet (aims to) maintain a set of replica Pods running at any given time.

• Pod Lifecycle - A high-level summary of what phase the Pod is in within its lifecyle.

• Pod Security Policy - Enables fine-grained authorization of Pod creation and updates.

• Selector - Allows users to filter a list of resources based on labels. Examples:

  • environment = production

  • tier != frontend

  • environment in (production, qa)

  • tier notin (frontend, backend)

• Service - An abstract way to expose an application running on a set of Pods as a network service.

• Service Account - Provides an identity for processes that run in a Pod.

• StatefulSet - Manages the deployment and scaling of a set of Pods, and provides guarantees about the ordering and uniqueness of these Pods.

• Static Pod - A pod managed directly by the kubelet daemon on a specific node.

• Volume - A directory containing data, accessible to the containers in a pod.