Docker

Stian Mathiassen

The Dream!

docker run myapp

Virtualization is NOT the point

Image and container

Image:

A snapshot of a disk image. Can be created by commiting a container.

Container

A program running in docker, which uses an image as a base image. Each container start from scratch from the base image.

Lifecycle in Docker

Get a base image

docker pull ubuntu:latest

Pulls an image from hub.docker.com

List all images

docker images


REPOSITORY TAG    IMAGE ID     CREATED     VIRTUAL SIZE
ubuntu     latest 9cd978db300e 7 weeks ago 204.4 MB

Image layers

Start a container

docker run ubuntu echo "Hello World"

Hello World

List containers

docker ps --all


CONTAINER ID IMAGE         COMMAND          CREATED       STATUS ...
2529384fabd4 ubuntu:latest echo Hello World 8 minutes ago Exit 0 ...

A useful container

docker run --interactive --tty ubuntu /bin/bash


root@a9f2bd405f9e:/# echo "Hello World" > /somefile.txt
root@a9f2bd405f9e:/# exit

Container has died

docker ps --all


CONTAINER ID IMAGE         COMMAND          CREATED        STATUS ...
a9f2bd405f9e ubuntu:latest /bin/bash        3 minutes ago  Exit 0 ...
2529384fabd4 ubuntu:latest echo Hello World 20 minutes ago Exit 0 ...

Restart a container

Will re-run the same command. Will re-use same disk.

docker start --attach --interactive a9f2bd405f9e


root@a9f2bd405f9e:/# echo "Hello World" > /anotherfile.txt
root@a9f2bd405f9e:/# exit

Diff changes to container

Will show changes from base image and the container

docker diff a9f2bd405f9e


A /.bash_history
A /anotherfile.txt
C /dev
C /dev/console
C /dev/core
C /dev/fd
C /dev/ptmx
C /dev/stderr
C /dev/stdin
C /dev/stdout
A /somefile.txt

Create a new image

Base the new image on a container. Will create a new layer on top of the base image

docker commit a9f2bd405f9e myimage:mytag


dbf0e2a6421dfcb3d2194c5e2c3daf2132bd0c172cdaaa3ab90f27d5a0273ba8

docker images --tree


└─511136ea3c5a Virtual Size: 0 B
  └─6170bb7b0ad1 Virtual Size: 0 B
    └─9cd978db300e Virtual Size: 204.4 MB Tags: ubuntu:latest
      └─dbf0e2a6421d Virtual Size: 204.4 MB Tags: myimage:mytag

Setup for assignment

We are using Vagrant for the assignments
Really just a virtual machine in VirtualBox
vagrant up Starts your virtual machine
vagrant destroy Resets your virtual machine
vagrant ssh Log in to the virtual machine
/vagrant inside the virtual machine is a shared folder

Assignment #1

Run echo "Hello world" in a container based on the Ubuntu image
Run an interactive bash in a container
Install node.js (nodejs) in a container (using interactive bash)

apt-get update Updates list of available software
apt-get install Install software

Create an image called assig1 with node.js installed
Try to run nodejs --version using your new image

Summary

docker run --interactive --tty ubuntu /bin/bash
(do stuff in container)
docker commit CONTAINER_ID

Dockerfile

The Recipe

Dockerfile


FROM ubuntu:latest
RUN apt-get update
RUN apt-get install -y nodejs npm

Each RUN-command creates a new layer. Layers are re-used

Build image

docker build --tag="ubuntu-nodejs" .


$> docker images
REPOSITORY     TAG      IMAGE ID      CREATED        VIRTUAL SIZE
ubuntu-nodejs  latest   34b580498f7b  2 minutes ago  248.2 MB

Assignment #2

Do the following using a Dockerfile ...

Create an image with nodejs and npm installed
Tag your image as ubuntu-nodejs
Create a container based on that image, and run nodejs --version to check that it is installed correctly

Dockerfiles pt. 2

ADD, ENTRYPOINT, USER, WORKDIR and EXPOSE

ADD

Copy a file from the host to the image


FROM ubuntu-nodejs

ADD ./src /var/apps/nodejs/

Same as running docker cp

USER

Run command as user


FROM ubuntu-nodejs
ADD ./src /var/apps/nodejs/

USER daemon

ENTRYPOINT

Command to run when starting the container


FROM ubuntu-nodejs
ADD ./src /var/apps/nodejs/
USER daemon

ENTRYPOINT ["nodejs", "/var/apps/nodejs/index.js"]

WORKDIR

Change current working directory


FROM ubuntu-nodejs
WORKDIR /
RUN rm -fr *

EXPOSE

Specify which ports the container should make available


FROM ubuntu-nodejs
ADD ./src /var/apps/nodejs/
USER daemon
ENTRYPOINT ["nodejs", "/var/apps/nodejs/index.js"]

EXPOSE 8888

Publish ports

Ports are not automatically published

docker run -p 8888:8888 ubuntu-nodejs

Maps ports 8888 on host machine to 8888 on container

Assignment #3

Based on the ubuntu-nodejs image created in Assignment #2:

Add /vagrant/app/src to /var/apps/nodejs inside the image
Run npm install in /var/apps/nodejs directory in the container
The application is started with nodejs /var/apps/nodejs/index.js
The application is running on port 8888
Start the container with the port mapped to port 8888 on the host machine
Check that the application is running on http://localhost:8888

Volumes

VOLUME

Add a data volume


FROM ubuntu:14.04
...
ENTRYPOINT mongod

VOLUME /data/db

Mounting volumes

docker run --volume /data:/data/db ubuntu-mongo

Linking containers

Container #1: MongoDB

FROM ubuntu:14.04

RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
RUN echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | sudo tee /etc/apt/sources.list.d/mongodb.list
RUN apt-get update
RUN apt-get --yes install mongodb-org

VOLUME /data/db
EXPOSE 27017

ENTRYPOINT mongod

$ docker build --tag ubuntu-mongo /path/to/mongodb/Dockerfile

$ docker run --volume /data:/data/db 
             --name mongodb 
             --detach ubuntu-mongo

MongoDB is running!

$ docker ps
CONTAINER ID  IMAGE         COMMAND               PORTS      NAMES
43a1d9173209  mongo:latest  /bin/sh -c mongod /b  27017/tcp  mongodb

Using --link to get environment properties


$ docker run -t -i --link="mongodb:mongodb" ubuntu bash

root@541474c8ccd4:/# env
...
MONGODB_PORT_27017_TCP=tcp://172.17.0.30:27017
MONGODB_PORT=tcp://172.17.0.30:27017
MONGODB_PORT_27017_TCP_PORT=27017
MONGODB_PORT_27017_TCP_PROTO=tcp
MONGODB_PORT_27017_TCP_ADDR=172.17.0.30
...

Using the environment variables

In our node app:


var mongoPort = process.env.MONGODB_PORT_27017_TCP_PORT;
var ip = process.env.MONGODB_PORT_27017_TCP_ADDR;

var connectionString = 'mongodb://' + ip + ':' + mongoPort + '/local';
mongoose.connect(connectionString);

Container #2: our NodeJS app

FROM ubuntu:14.04

RUN apt-get update
RUN apt-get --yes install nodejs npm

ADD ./src /var/apps/nodejs/
RUN cd /var/apps/nodejs/; npm install

EXPOSE 8888

CMD nodejs /var/apps/nodejs/index.js

$ docker build --tag ubuntu-nodejs /path/to/nodejs/Dockerfile

$ docker run --publish 8888:8888 
             --link="mongodb:mongodb" 
             --detach ubuntu-nodejs

Our Nodejs app is now connected to MongoDB


$ docker ps
IMAGE                 COMMAND               PORTS                    NAMES
ubuntu-nodejs:latest  /bin/sh -c 'nodejs /  0.0.0.0:8888->8888/tcp   lonely_goldstine
mongo:latest          /bin/sh -c mongod /b  27017/tcp                drunk_ptolemy/mongodb,lonely_goldstine/mongodb,mongodb

Assignment #4

Build an image with MongoDB running
(Create the new Dockerfile in a seperate directory. Remember to EXPOSE the port)
Run a container based on the newly created Mongod-image
(remember to give it a --name)
Start the Nodejs application with the --link option
Verify that the application is connected to MongoDB by visiting http://localhost:8888

Bonus assignment

Build images that you find useful!

https://hub.docker.com/

Building on Docker

Docker compose - Container management
Kubernetes - PaaS by Google
Dokku - Mini-PaaS in 100 lines of bash
Deis - PaaS
Flynn - PaaS

Docker

The Dream!

Virtualization is NOT the point

Image and container

Image:

Container

Lifecycle in Docker

Get a base image

List all images

Image layers

Start a container

List containers

A useful container

Container has died

Restart a container

Diff changes to container

Create a new image

Setup for assignment

Assignment #1

Summary

Dockerfile

The Recipe

Dockerfile

Build image

Assignment #2

Dockerfiles pt. 2

ADD

USER

ENTRYPOINT

WORKDIR

EXPOSE

Publish ports

Assignment #3

Volumes

VOLUME

Mounting volumes

Linking containers

Container #1: MongoDB

Using --link to get environment properties

Using the environment variables

Container #2: our NodeJS app

Our Nodejs app is now connected to MongoDB

Assignment #4

Bonus assignment

Building on Docker

Thank you!

Stian Mathiassen