Overview

Docker is the container format used by OpenShift v3

OpenShift uses Kubernetes as a docker orchestrator

The OpenShift “stack” (top to bottom):

Definitions

Docker image: A file system image for running an process/application
Docker Container: A running instance of a docker image
Pod: Kubernetes object that groups related containers that need to share network file system or memory for placement on a node. You can run multiple instances of a pod
Replication Controller: Kubernetes Object that ensures N instances of a give pod are running at all times
Service: Kubernetes object that provides load balanced access to multiple pods. Services are only available INSIDE OpenShift, not user facing.
Route: An OpenShift route is a way to expose a service by giving it an externally-reachable hostname like www.example.com

A single pod gets an IP address and can run multiple docker containers.

All containers in a pod share pod ports, no conflicts allowed and IP address

A pod an run one or more containers

OpenShift also has the idea of a service.

A physical host will run one or more pods

A service load balances multiple instances of a single pod

All containers in a POD start and stop at the same time.

Question: Can PODS span hosts? I don’t think so…

Services have a label such as “web”

Developers interact with the Web Console, CLI and service Layer. Users see the Routing Layer

You Expose you application via “route”

There’s three application deployment options: