Docker

Introduction

by

Marek Goldmann

10th Dec 2013

Docker?

A project to create and manage containers.

Containers?

Yes, a lightweight operating system virtualization.

How this compares to a virtual machine?

It's completely different.

Comparison

Who's behind Docker?

dotCloud* and a powerful community.

* dotCloud, Inc. was recently renamed to Docker, Inc.

Speaking of community...

• GitHub
  • 501 watches
  • 6948 stars
  • 847 forks
  • 406 open issues
  • 69 pull requests
• Over 200 contributors
  • avg 13 commits / day
  • 92% are external
• Many meetups all over the world
  • 15 active meetup groups

Achieved after 10 months since first commit to GitHub

Glossary

• Image: a package with filesystem and data
• Container: a running image
• Registry: place where images are hosted/shared

Main concepts

• An image can be linked to a parent image
• Image not having a parent is called base image
• Container has a state, whereas image doesn't
• You can launch multiple containers from an image

Docker components

Creating Docker images

It's simple! Use Dockerfiles.

Dockerfile

A plain text file with instructions that automate building the image.

Dockerfile example

# Base on the Fedora 20 image
FROM mattdm/fedora

# Upgrade the image
RUN yum -y update

# Install java
RUN yum -y install java-1.7.0-openjdk-devel wget

# Get WildFly
RUN wget http://download.jboss.org/wildfly/8.0.0.Beta1/wildfly-8.0.0.Beta1.tar.gz -O /opt/wildfly.tar.gz
RUN tar -xf /opt/wildfly.tar.gz -C /opt

# Run WildFly after container boot
ENTRYPOINT /opt/wildfly-8.0.0.Beta1/bin/standalone.sh -c standalone-ha.xml -b 0.0.0.0
					

This should be saved as Dockerfile

Basic instructions

• FROM: the image we're basing on / extending
• RUN: The command to execute at the build time
• ENTRYPOINT: The command to be executed after the container boot

But there is a lot more!

Building the image

Building the image

$ docker build .
Uploading context 10240 bytes
Step 1 : FROM mattdm/fedora

[SNIP]

Step 4 : RUN wget -q http://download.jboss.org/wildfly/8.0.0.Beta1/wildfly-8.0.0.Beta1.tar.gz -O /opt/wildfly.tar.gz
 ---> Running in 41467b97b423
 ---> 112766c23202
Step 5 : RUN tar -xf /opt/wildfly.tar.gz -C /opt
 ---> Running in d07d0c5c3dab
 ---> c53f9f4ceb1e
Step 6 : ENTRYPOINT /opt/wildfly-8.0.0.Beta1/bin/standalone.sh -c standalone-ha.xml -b 0.0.0.0
 ---> Running in a9b2cecf4db5
 ---> 5894688e4f2e
Successfully built 5894688e4f2e
          

We've built image 5894688e4f2e

Modifyng the image

1. Change the Dockerfile
2. Execute the build command once again

Let's talk about speed

$ time docker build .
Uploading context 10240 bytes
Step 1 : FROM mattdm/fedora
 ---> 0f3e92b4e94d

[SNIP]

Step 4 : RUN wget -q http://download.jboss.org/wildfly/8.0.0.Beta1/wildfly-8.0.0.Beta1.tar.gz -O /opt/wildfly.tar.gz
 ---> Using cache
 ---> 2ad6655478dd
Step 5 : RUN tar -xf /opt/wildfly.tar.gz -C /opt
 ---> Using cache
 ---> c0f63f06e9ec
Step 6 : RUN touch /etc/something
 ---> Running in 8426dd5570af
 ---> 7ef016a00cde
Step 7 : ENTRYPOINT /opt/wildfly-8.0.0.Beta1/bin/standalone.sh -c standalone-ha.xml -b 0.0.0.0
 ---> Running in 60bfa9d3a746
 ---> e757e0ea05d7
Successfully built e757e0ea05d7

real  0m0.307s
user  0m0.000s
sys 0m0.018s
          

We've built a new image e757e0ea05d7

Yes, 300ms!

How does it work

1. Prepare to execute an instruction
   • Was the instruction executed before?
     • yes - use the previous result, go to #3
     • no - execute the instruction, go to #2
2. Was the instruction executed without error?
   • yes - commit, go to #3
   • no - fail the build
3. Is this the end of instructions?
   • yes - commit, finish!
   • no - go to #1

Let's talk about size

$ docker images

REPOSITORY          TAG                 ID                  CREATED             SIZE
<none>              <none>              e757e0ea05d7        37 minutes ago      12.29 kB (virtual 1.056 GB)
<none>              <none>              5894688e4f2e        46 minutes ago      12.29 kB (virtual 1.056 GB)
					

Yes, 12.29kB!

Image repositories

1. Private: for example hosted inside a company
2. Public: index.docker.io

Docker CLI commands

docker pull

Pull image or repository to the registry

docker push

Push image from registry to a repository

docker run

Run a command in a new container based on the specified image

docker stop

Stop a container

docker start

Start a stopped container

docker rm

Remove a stopped container

docker rmi

Remove an image from registry

OK, great, but...

Use-cases?

• Want your own PaaS?
• Automated testing and CI
• Deploying scalable apps
• Application delivery platform

PaaS

It's (fairly) easy to create a PaaS with Docker

There is even a tutorial to create one in 5 minutes...

OpenShift

https://github.com/openshift/openshift-pep/blob/master/openshift-pep-010-docker-cartridges.md

Continuous Integration

1. You commit
2. CI builds the app
3. CI creates an image with the new app
4. CI starts a container from new image
5. Integration tests are executed on a real application
6. Profit!

Scalable apps

• Requirement: prepare your app to be easily scalable
• Starting a container is fast and cheap
• Extending a (for example WildFly) cluster is easy
• Profit!

Delivery platform

Build once - run anywhere!

• Downloading is easy and fast
• Upgrading images is easy too

Profit!

Where to start?

yum install docker-io

http://docs.docker.io/en/latest/use/basics/

Thanks!

Attributions:

• https://www.docker.io/