Kubernetes

Contents

Basic Objects

  • pod - container / set of containers + storage resources + unique IP + local options

  • service - abstraction layer on top of a set of ephemeral pods (think of this as the 'face' of a set of pods)

  • volume - sometimes-shared, persistent storage

  • namespace - virtual cluster on top of an underlying physical cluster

Service Types

  • clusterIP - exposes services only inside the cluster (default)

  • nodePort - exposes services at the specified port on all nodes (:)

  • loadBalancer - exposes the service with a cloud-provider's load balancer.

  • externalName - this maps a service to endpoints completely outside of the cluster

Controllers

  • replicaSet - ensures a certain number of pods are running

  • deployment - declaratively manages a replicaSet

  • statefulSet - like a deployment, but for non-interchangeable (or stateful) underlying pods

  • daemonSet - manages pods that need to run on all/some nodes

  • job - manages a set of pods that run to completion and tracks the overall progress

Control Plane

  • master - entity responsible for managing cluster state. It consists of 3 major components:

  • kube-apiserver - exposes cluster control and state

  • kube-controller-manager - this is where the 'brain' of controllers live

  • kube-scheduler - matches resources to work

  • node - individual machines or VMs that make up the cluster. A node consists of:

  • kubelet - service that communicates with the master

  • kube-proxy - proxy for connecting to the cluster network

namespace -> virtual cluster on top of an underlying physical cluster