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Docker, Kubernetes & OpenShift

Build, containerize & orchestrate

Marko Lukša, Red Hat

mluksa@redhat.com

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Docker

  • Platform for building, distributing and running applications
  • Lightweight container virtualization
  • 10s of VMs => 100s, 1000s of containers per host

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Docker concepts

  • Images
    • A read-only package of an app & environment
    • Consists of Layers (some layers shared by images)
  • Registries
    • Pull images from & push images to registry
    • Private & public registries (Docker Hub)
  • Containers
    • A running image (“Process in a box”)
    • Read-Write layer on top of base image

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Docker layers

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Creating Docker images

  • Use existing image (e.g. fedora, jboss/wildfly)
  • Run a command (anything, even a shell)
    • Docker creates a new container from image
    • Allocates a read-write layer on top of image
    • Executes the command
  • Run additional commands
  • Look up last container id
  • Commit the container as new image

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Dockerfile

  • Build an image automagically
  • Specifies base image and instructions:
    • FROM <existing image>
    • ADD <local file> <path inside image>
    • RUN <cmd>
    • EXPOSE <port>
    • ENV <name> <value>
    • CMD <cmd>

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Dockerfile - example

# Use latest jboss/base-jdk:7 image as the base�FROM jboss/base-jdk:7��# Set the WILDFLY_VERSION env variable�ENV WILDFLY_VERSION 8.1.0.Final��# Add the WildFly distribution to /opt�RUN cd $HOME && curl http://download.jboss.org/wildfly/$WILDFLY_VERSION/wildfly-$WILDFLY_VERSION.tar.gz | tar zx && mv $HOME/wildfly-$WILDFLY_VERSION $HOME/wildfly��# Set the JBOSS_HOME env variable�ENV JBOSS_HOME /opt/jboss/wildfly��# Expose the ports we're interested in�EXPOSE 8080 9990��# Set the default command to run on boot�CMD ["/opt/jboss/wildfly/bin/standalone.sh", "-b", "0.0.0.0"]

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Kubernetes

  • Orchestration system for Docker containers
  • Provides basic mechanisms for:
    • deployment
    • maintenance
    • scaling
  • Auto-restarting, re-scheduling & replicating containers

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Kubernetes architecture

  • Master node
    • etcd (distributed key value store)
    • Kubernetes API Server (REST) (+ Scheduler)
    • Kubernetes Controller Manager Server
  • Minions
    • Docker
    • Kubelet
    • Kubernetes Proxy

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Kubernetes concepts

  • Pods
  • Volumes
  • Labels
  • Replication controllers
  • Services

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Pods

apiVersion: v1beta1

id: www

desiredState:

manifest:

version: v1beta1

id: X

containers:

- name: nginx

image: dockerfile/nginx

- name: mydb

image: foo/mycooldb

​

Minion (Host) 1

A

Pod X

B

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Pods (continued)

  • Resource sharing & communication
  • Not fully isolated
  • Scheduled to a node
  • Containers are auto-restarted
  • If a node dies, its pods are deleted (not rescheduled)

Minion (Host) 1

A

Pod X

B

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Volumes

desiredState: manifest:

containers:

- name: A

image: foo/A

volumeMounts:

- name: vol1

mountPath: /data/vol1

volumes:

- name: vol1

source:

emptyDir: {}

Or:

hostDir: /opt/data/vol1

Minion (Host) 1

A

Pod X

B

Vol 1

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Labels

  • key-value pairs
  • for categorizing things

“env”:”dev”, “env”:”prod”, “env”:”qa”

“rel”:”stable”, “rel”:”canary”

“partition”:”custA”, “partition”:”custB”

  • label selectors

​

Minion (Host) 1

A

Pod X

B

Vol 1

“name”: “podX”,

“env”: “dev”

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Replication controllers

id: replicationControllerY

kind: ReplicationController

desiredState:

replicas: 2

replicaSelector:

env: prod

rel: stable

podTemplate:

desiredState:

manifest:

...

labels:

- env: prod

- rel: stable

​

​

Minion (Host) 1

A

Pod X

Minion 2

Replication controller Y

(replicas: 2, podTemplate, replicaSelector: {“env”:”prod”, “rel”:”stable”})

B

Vol 1

“name”: “podX”,

“env”: “dev”

C

D

Pod Y1

“env”: “prod”,

“rel”: “stable”

​

C

D

Pod Y2

“env”: “prod”,

“rel”: “stable”

​

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Services

id: myApp

kind: Service

apiVersion: v1beta1

port: 1234

selector:

env: prod

containerPort: 2345

​

  • Env vars: MYAPP_SERVICE_HOST, MYAPP_SERVICE_PORT
  • future: DNS

​

​

Minion (Host) 1

A

Pod X

Minion 2

Replication controller Y

(replicas: 2, podTemplate, replicaSelector: {“env”:”prod”, “rel”:”stable”})

B

Vol 1

“name”: “podX”,

“env”: “dev”

C

D

Pod Y1

“env”: “prod”,

“rel”: “stable”

​

C

D

Pod Y2

“env”: “prod”,

“rel”: “stable”

​

myApp (selector: {env:prod})

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Phased rollout / canary releases

  • New replication controller (rel:canary)
  • stable controller: replicas--
  • canary controller:�replicas++

Minion (Host) 1

A

Pod X

Minion 2

Replication controller Y

(replicas: 1, podTemplate, replicaSelector: {“env”:”prod”, “rel”:”stable”})

B

Vol 1

“name”: “podX”,

“env”: “dev”

Replication controller Y’ (replicas: 1, podTemplate, replicaSelector: {“env”:”prod”, “rel”:”canary”})

C

D

Pod Y1

“env”: “prod”,

“rel”: “stable”

​

myApp (selector: {env:prod})

​

“env”: “prod”,

“rel”: “stable”

​

C

D

Pod Y2

C’

D’

Pod Y’1

“env”: “prod”,

“rel”: “canary”

​

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Remove/debug malfunctioning pod

  • labels of a running pod can be changed
  • way of adding or removing pods from services or replication controllers

Minion (Host) 1

A

Pod X

Minion 2

Replication controller Y

(replicas: 2, podTemplate, replicaSelector: {“env”:”prod”, “rel”:”stable”})

B

Vol 1

“name”: “podX”,

“env”: “dev”

C

D

Pod Y1

“env”: “prod”,

“rel”: “stable”

​

myApp (selector: {env:prod})

​

“env”: “prod”,

“rel”: “stable”

​

C

D

Pod Y2

C

D

Pod Y3

“env”: “prod”,

“rel”: “stable”

​

“env”: “debug”,

“rel”: “stable”

​

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OpenShift v3

  • Platform-As-A-Service
  • Kubernetes extensions
    • Application Templates
      • Single JSON file for configuring Kube resources
      • Parameterizable (see example)
    • Builds
      • Hosts source code in git repos
      • Performs builds and hosts private docker images
      • Kick off new builds on git-push

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Resources

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