Docker Repository

This repository collects all the sources used to build the docker images used to run certain jobs. The main rule to keep a fast pace when building an image is to keep only the strictly necessary files in the current folder.

Repository Structure

Under dockerfiles folder are stored all the sub-folders named after the image they generate. Each of these sub-folders contains the self-comprehensive build context imported by docker during a build task.

To ease a post-configuration of an image is possible to create ad-hoc configuration files from the conf_template folder (e.g. ssh host configurations).

Install Docker

On Debian is available a dedicated *.deb package. Follow the instructions at this page.

Docker by default stores all the generated artifacts (images/containers/volumes/networks) into the default folder /var/lib/docker/. If the space required is bigger than what available on the mentioned folder, one trick consist in mounting a folder created on a more spacious file-system and bind it to the docker destination folder.

This can be achieved by adding the following line to the /etc/fstab file:

<large_space_folder> /var/lib/docker/ none defaults,bind 0 0

Uninstall Docker

To uninstall a docker installation execute the following command:

# old versions
sudo apt remove docker docker-engine docker.io containerd runc
# new versions
sudo apt remove docker-ce docker-ce-cli containerd.io

It is not a problem if apt reports that some of them are not installed at all (it is referred to older versions).

Moreover to completely remove all images/containers/volumes/networks, remove the /var/lib/docker/ folder (original docker content destination folder):

sudo rm -rf /var/lib/docker

Docker How-To

The following sections collect some nice tricks to efficiently take care of the images in docker. In order to let your user to use docker without the use of sudo, add your user to the docker group:

sudo usermod -a -G docker <your_login>

Remember to logout and login again in your user account for this setting to take effect.

Build Images

Before building an image be sure to execute the initialization script that copies the common scripts in the scripts sub-folders of each target-image. Hence the usual command to build the image itself:

./init-build.sh
sudo docker build -t <name-image>:<tag> <context-source>

Where the <context-source> is the folder from which the docker daemon will get its context, i.e. ./dockerfiles/<target-context>.

The initialization script copies the scripts only in those targets that require them. To add a new environment to the list modify the init-build.sh script.

Running Images

When running an image it is always advisable to mount the folder the job should be performed on in the image. In this way the created docker container can perform its job and the sources/results will all co-exist in the mounted volume:

sudo docker run --rm -ti -v "$(pwd)":/home/developer/work <docker-image>

The --rm will remove the container once closed, the -ti are two independent flags to allocate a pseudo-tty and to keep the container open and interactive when run.

Mounting a volume also allow the container to share resources with the host machine. For instance the X11 socket to show programs GUIs. In the example below, two volumes are mounted, one to let the container work on the current directory and one to make a 1-to-1 mapping of the host X11 socket into the container socket (ro read only to prevent the image from corrupting the host socket):

sudo docker run --rm -ti -v "$(pwd)":/home/developer \
       -v /tmp/.X11-unix:/tmp/.X11-unix:ro -e DISPLAY=$DISPLAY \
       <docker-image>

In Windows properly set the DISPLAY variable will suffice (no X11 volume mapping required). Configure the VcXsrv Windows X Server software. Make sure the OS variable is set to the internal gateway address such that the X11 server can listen to the docker container requests.

Follow this guide to have more info and ensure the container can access the user X Window process: https://www.cbtechinc.com/desktop-docker-1-linux-graphical-containers/

Cleaning Up

There are few commands to free up some space when getting the error no space left on device.

Delete All At Once

This will delete all containers that were stopped as well as all volumes and networks and that are not used by any container. It will also remove all dangling images:

docker system prune

Deleting Dandling Images Only

When using the same name:tag combinations to try out different partial images, the local registry will be cluttered with orphan <none> image steps. To clear out them use the following

docker rmi -f $(docker images -f "dangling=true" -q)

The -f option force the removal, it might be required (and often suggest by the tool itself).

todo:

• reinstall docker on your drive to have access to a way larger volume