Basics

• A container is an instance of an image (e.g running image)

Installation

Currently, on Linux mint, don't use the apt-get package, but the installation procedure on the Docker page. To be able to run docker as a user:

sudo usermod -aG docker axelle

Then unlog/relog.

Commands

• docker images: shows all existing images on your host
• docker search: to search for (public) images:

  docker search --stars=10 debian
  

• docker pull: to download a given image:

  docker pull docker/whalesay
  

• docker run: to run a given image (-> container):

  $ docker run hello-world
  

• docker ps: list all running containers. If you specify docker ps -a, you'll list all containers even those which have exited.
• docker stop container: stops a container
• docker rmi: removes an image. For example:

  docker rmi -f tag
  

• docker logs container: view logs of the container. Add -f to follow the flow of logs
• docker inspect container: view the configuration of a given image or container

What's my container id?

If you are running an interactive shell in the container, then the container id shows in the prompt:

root@deffbaefb43f <- that's the container id

You can also get the id with docker ps -a.

Details

Copying a file to the container

cp thefile.txt /var/lib/docker/devicemapper/mnt/123abc/rootfs/root 

Creating a data container

The following container merely creates two directories in which data will be held:

docker create -v /usr/src/redmine/config -v /usr/src/redmine/files --name redmine-data redmine /bin/true

Port forwarding or redirection

In this case, the container redirects port 9000 to 8000 to the external world:

$ docker run -d -p 8000:9000 ...

If there are several ports to redirect, add as many -p directives. If the port should not redirected, but still open: -p 9000:9000 for example.

Running an interactive container

It's the -i option in docker run. The typical command which is very much used is:

docker run -t -i container /bin/bash

The -t gets a tty. And this command will get an interactive shell in the container. You can also use:

docker exec -it container bash

Virtualize MAC address

$ docker run -d ... --mac-address="00:11:22:33:44:55" blah/blah

Launching a server automatically

When launched with "docker run", a container exits as soon as the command returns. If we want the container to remain alive, the idea is to launch the container with a command that does not return. To do so, a solution is to use "supervisord":

sudo apt-get install supervisor

Then in /etc/supervisor/conf.d, create a configuration file for the service to launch:

command=...
autostart=true
autorestart=false
stderr_logfile=/var/log/blah.err.log
stdout_logfile=/var/log/blah.out.log

and in /etc/supervisor/supervisor.conf, add:

[supervisord]
nodaemon=true

Then, you should refresh supervisor:

$ supervisorctl reread
$ supervisorctl update

Check your service runs ok:

$ supervisorctl

If not, check the logs. Then, run your docker container like:

$ docker run -d ... container /usr/bin/supervisord

Docker file

ROM debian:wheezy
MAINTAINER name 
RUN apt-get update 
COPY nginx.conf /etc/nginx/nginx.conf
RUN chmod 744 /home/docker/script/service_start.sh
ENTRYPOINT /home/docker/script/service_start.sh
WORKDIR /home/docker

The ENTRYPOINT is to start when the container starts.

Building

docker build -t name .

Backup

To backup an image:

$ docker save -o ~/container1.tar container1

To restore:

$ docker load -i /container1.tar

To backup a container, the idea is to perform a commit:

$ docker commit container-id name

Interesting images

• debian