What is Docker?

Docker is not...

Virtual Machines

Magic

What is Docker?

Docker creates isolated environnements (called containers) to isolate applications.

How it works?

Docker stands on Linux kernel, Linux namespaces (isolated environments) and on Linux cgroups (resource management memory/cpu/disk)

How it works?

Docker is not Virtual Machines

What is a container?

It's all about isolation

• Isolated filesystem
• Isolated users
• Isolated process
• Isolated networks

As close as possible to a standard Linux installation...

but runs on the Host's Kernel

Docker images

• An image is like a container snapshot (static/read-only).
• A container is the instanciation of an image.
• Images have base images.
• Images are layered.
• Images are taggued

Docker images

Docker images

• debian:jessie : Contains debian-jessie libs/apps
• buildpack-deps:jessie-curl : Contains curl
• openjdk:8-jre : Contains OpenJdk JRE 8
• tomcat:9.0-jre8 : Contains Tomcat 9

Docker images

user@host:~$ docker images
REPOSITORY        TAG            IMAGE ID        CREATED        SIZE
tomcat            9-jre8         345a325b9d4f    2 weeks ago    334.9 MB
openjdk           8-jre          b13ebf1a4999    3 weeks ago    311.2 MB
buildpack-deps    jessie-curl    187e81a2e1ae    3 weeks ago    167.3 MB
debian            jessie         73e72bf822ca    3 weeks ago    123 MB

Docker ecosystem

How to use docker?

How to use docker

Main commands

• docker pull : get an image from the registry
• docker build : create an image from a Dockerfile
• docker create : create a container from an image
• docker run : creates a container from an and starts it
• docker start/stop : starts/stops containers
• docker commit : creates an image from a running container
• docker logs : fetch the logs af a container (stdout/stderr)

Working with images

• docker pull imageName:tag : get an image from the registry
• docker build : create an image from a Dockerfile

Working with images

Building an image from a Dockerfile

Dockerfile : File describing the construction steps of an image

FROM debian:jessie

RUN echo 'deb http://deb.debian.org/debian jessie-backports main' > /etc/apt/sources.list.d/jessie-backports.list

ENV JAVA_DEBIAN_VERSION 8u111-b14-2~bpo8+1

RUN apt-get update \
	&& apt-get install -y openjdk-8-jre-headless="$JAVA_DEBIAN_VERSION"

ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64/jre

user@host:~$ docker build --tag myJRE:1.0 .

Working with images

Listing images

user@host:~$ docker images
REPOSITORY        TAG            IMAGE ID        CREATED        SIZE
tomcat            9-jre8         345a325b9d4f    2 weeks ago    334.9 MB
openjdk           8-jre          b13ebf1a4999    3 weeks ago    311.2 MB
buildpack-deps    jessie-curl    187e81a2e1ae    3 weeks ago    167.3 MB
debian            jessie         73e72bf822ca    3 weeks ago    123 MB

Working with images

Removing images

user@host:~$ docker rmi tomcat:9-jre8
Untagged: tomcat:9-jre8
Deleted: sha256:345a325b9d4ff4e3ceb5239f706c32f6058111bf101bfab4ea2386aaa9a58afa
Deleted: sha256:edd8f93b163a01e11c701c65cf24373ef0326a40692cf848e963b3c9b56e9619
Deleted: sha256:ad145ed46bd12e51afacbc9313fbf51ea9af1b451434f3761c993c14440aacff
Deleted: sha256:6976e3f3625b4467efa53b04a24fb1a97741b4125291f115ebc79d7a545650d7
Deleted: sha256:66db73f2947c39132e728c6f263ddeef0b9bc3262b4022560eb82bcb1a1f55fb
Deleted: sha256:78780b79263b4913e74e1855dd55f8f2e65ff848fb7582c3c76af88789e55f3a
Deleted: sha256:bd20af890581a5af2c1ab5b4d9ab095833142878600edd91fea639e641129cd9

Working with containers

Running a container from an image

user@host:~$ $ docker run --tty --interactive debian:jessie

Creates a container, attaches an interactive shell

user@host:~$ $ docker run debian:jessie echo Docker is fun

Creates a container, runs the command echo Docker is fun and exits

user@host:~$ $ docker run --rm debian:jessie echo Docker is fun

Creates a container, runs the command echo Docker is fun and deletes the container

Working with containers

Creating a container from an image

user@host:~$ $ docker create -p 5432:5432 --name myPostgresInstance postgres

Creates a container, maps host port 5432 to container port 5432 and names the container

user@host:~$ $ docker start myPostgresInstance

Starts the container

user@host:~$ $ docker start myPostgresInstance

Working with containers

user@host:~$ $ docker create -p 5432:5432 --name myPostgresInstance postgres

user@host:~$ $ docker start myPostgresInstance

Where is my data ?

Inside the container filesystem!

Working with containers

Binding filesystem

user@host:~$ $ docker create \
    -p 5432:5432 \
    -v /data/postgres:/var/lib/postgresql \
    --name myPostgresInstance postgres

Creates a container, maps host port 5432 to container port 5432 and names the container

The container directory /var/lib/postgresql is mapped to the host directory /data/postgres