hkdigital/debian-slim repository overview

⁠About

This docker image extends the image debian:bullseye-slim⁠.

Some useful basic tools are installed that are often used by installers and scripts. This image is not intended to be the smallest debian base image, but as a useful image for development, testing and most common production environments.

The image uses dumb-init⁠ as ENTRYPOINT, which overrides the default /bin/sh -c.

A default CMD /srv/run.sh is specified, a script that executes sleep infinity.

⁠Usage

⁠Start using "docker run"

⁠Run "sleep infinity" inside the container

Run a container:

docker run --rm hkdigital/debian-slim

This command will create a docker container, run the default CMD /srv/run.sh inside the container and remove the container when the script finishes.

By default /srv/run.sh will execute the command "sleep infinity", so it won't finish. Press ctrl-c to quit the script and to stop and remove the container.

⁠Run a bash shell inside the container

Run the following command to run an interactive bash shell:

docker run -ti --rm hkdigital/debian-slim bash

A bash shell opens and you're free to do whatever you want. To exit the bash shell, type exit. Note that the container will be removed when the bash shell exits. Configuration or installed programs in the container will be lost.

Note that the script run-tmp-bash-container.sh, which is included in this project, do nothing more than the command shown above.

⁠Run using "docker-compose"

Below an example is shown of how the image can be used in a docker-compose file. The image will be downloaded from Docker Hub⁠.

Note that the container will execute the default CMD. The default CMD executes sleep infinity, so the container will not terminate until you stop the container or press ctrl-c to stop the script.

docker-compose.yml

version: "3.9"

services:
  debian:
    image: hkdigital/debian-slim

Open two terminals and go to the directory where the docker-compose.yml file resides.

In the first terminal start the container:

docker-compose up

Use the second terminal to stop and remove the container:

docker-compose stop
docker-compose rm

⁠Run bash in an existing and running container (docker-compose)

Use the following command to execute bash inside a running container (e.g. started like explained above).

You can use this when you need a disposable linux environment to try things out.

docker-compose exec debian bash

Type exit to quit.

⁠Environment variables from file

The run.sh command calls a script expand-file-environment-vars.sh. This script detects environment variables the end with _FILE and than reads the contents of the file specified by that variable into a new environment variable.

e.g. when defining in the docker-compose (stack) yaml file

service:
  my_service:
    environment:
      SECRET_FILE: /run/secrets/SECRET

The environment variable SECRET will be set that contains the contents of the file at /run/secrets/SECRET.

⁠Docker Swarm Secrets

The main reason why the environment _FILE variables are supported is for Docker Swarm.

When creating your own image, call the ./expand-file-environment-vars.sh from your run.sh. This way, the contents of Docker Secrets files will be loaded into environment variables.

The _FILE appendix is not a Docker standard, but generally accepted as a good approach.

A complete Docke Swarm stack example:

version: '3.9'  # use a modern version, otherwise secrets won't work

secrets:
  SECRET:
    external: true

service:
  my_service:
    secrets:
      - SECRET

    environment:
      SECRET_FILE: /run/secrets/SECRET

⁠Extend the image

Specify the name of this image in the FROM command of your Dockerfile.

FROM hkdigital/debian-slim
...

⁠Tag your image and push the image to docker hub

If your image is ready, you might want to publish it, so it can be downloaded from a central location, for example Docker Hub⁠.

To publish the image, you need two commands: docker tag and docker push.

If you want to push to Docker hub, you must setup a (free) docker hub account and create the repository first.

docker tag <existing-image> <hub-user>/<repo-name>[:<tag>]
docker push <hub-user>/<repo-name>:<tag>

e.g.

docker tag acme-foo-image acme/foo-image
docker push acme/foo-image

See also Docker hub repositories⁠

If you're a paying user of Docker Hub, you can also publish images automatically from e.g. a GitHub or BitBucket repository.

⁠Build locally

If you just want to use the image to create a container, there is no need to build the image locally. You can use the image from docker-hub.

Building the image locally is usually done for development of the image itself.

⁠Get a working copy from the repository

Clone the latest commit from github into a local working directory.

git clone --depth 1 \
  [email protected]:hkdigital/docker-images--debian-slim.git \
  hkdigital-debian-slim

⁠Build the docker image

./build-latest-image.sh
docker image ls
# Shows hkdigital-debian-slim