Kubernetes Concepts

From NovaOrdis Knowledge Base
Jump to: navigation, search

External

Internal

Overview

Kubernetes is an container orchestration platform, offering the ability of orchestrate Docker containers across multiple hosts. It manages containers in a clustered environment. It orchestrates containers at scale, defines application topologies, handles parts of the container networking, manages container state and schedules containers across hosts.

Master

OpenShift Master

Node

OpenShift Node

Pod

OpenShift Pod Concepts

Storage

Persistent Volume

https://kubernetes.io/docs/concepts/storage/persistent-volumes/

Represented by a PersistentVolume object. It is associated with a project.

An administrator provision persistent volumes from sources such as:

  • NFS
  • GCE Persistent Disks
  • ESB Volumes
  • GlusterFS
  • OpenStack Cinder
  • Ceph RBD
  • iSCSI
  • Fiber Channel

Storage resources are requested by laying a claim to the resource (PersistentVolumeClaim). A persistent volume claim is a request for a resource with a specific attributes. When a request is made, a process matches it to an available volume and binds them together. The runtime finds the volume bound to the claim and mounts it into the pod.

Persistent volumes can be recycled after use. The reclamation policy is based on the "persistentVolumeReclaimPolicy" declared in the PersistentVolume object definition. The policy can be "Retain" or "Recycle".

OpenShift Persistent Volume

etcd

A distributed key/value datastore for state within the environment.

etcd

Scheduler

OpenShift Scheduler

Namespace

A namespace provides scope for:

  • named resources to avoid naming collisions
  • delegating management authority to trusted users
  • the ability to limit community resource consumption
OpenShift Project

Policies

Policies are rules that specify which users can and cannot specify actions on objects (pods, services, etc.).

OpenShift Policies

Service

https://docs.openshift.com/container-platform/3.5/architecture/core_concepts/pods_and_services.html#services
OpenShift Service
Relationship between a Service and an OpenShift Router

Service Definition File

Service Definition File

API

OpenShift API

Label

OpenShift Label

Selector

OpenShift Selector

Replica

A replica is a set of pods sharing the same definition.

Replication Controller

OpenShift Replication Controller

Replication Controller Definition File

Replication Controller Definition File

Deployment

Deployment