Docker Entrypoint

Simple setup of Docker containers during initialization.

If you are reading this, chances are you know Docker and have been playing around with it. If that is the case, I can skip the introductions about containers -- which I will anyways -- and go straight to the point.

We know containers are awesome, and also that they are not exactly designed to offer dynamic environment. For instance, if one doesn't want to run the container as root, (s)he will have to setup a user during docker-build. If your container is meant to run a standalone service that's fine, but if you use containers like me, interactively, and containers became your standard testing environment for every new tool, then a bit of dynamism during initialization sounds good, right?

And that's why I wrote this entrypoint.sh script, to have some automation during container's initialization. Basically, I want to have the possibility of decide my user credentials during container's call, and have an adequate (container) environment for that. It understands and act accordingly to the following environment variables:

• DOCKER_USER: defines the name of user (default is 'user')
• DOCKER_UID: defines the user UID (default is '1000')
• DOCKER_GID: defines the user's group GID (default is '100')
• NOUSER: run the container as root
• WORKDIR: set a work directory (default is '/work')
• EXECAPP: set the executable/app to run (default is '/bin/bash')

The entrypoint.sh script is meant to be used as a container's ENTRYPOINT.

How to use it

With Git

Put at the end of your Dockerfile:

RUN git clone -b stable https://github.com/chbrandt/docker_entrypoint.git && \
    ln -sf docker_entrypoint/entrypoint.sh /.

ENTRYPOINT ["/entrypoint.sh"]

With Curl

Put at the end of your Dockerfile:

RUN curl -O https://raw.githubusercontent.com/chbrandt/docker_entrypoint/stable/entrypoint.sh && \
    chmod a+x docker_entrypoint/entrypoint.sh && \
    ln -sf docker_entrypoint/entrypoint.sh /.

ENTRYPOINT ["/entrypoint.sh"]

Entrypoint

entrypoint.sh setup a user and a work directory with the proper permissions. If the image where entrypoint.sh is being used has a EXECAPP defined, the entrypoint.sh executes EXECAPP by the requested user, at WORKDIR using the positional arguments given through docker run command.

user setup

When running the docker run command, the user can specify a user name, uid and gid through the variables DOCKER_USER, DOCKER_UID, DOCKER_GID, respectively.

For example:

# docker run -it -e DOCKER_USER='brandt' -e DOCKER_UID=500 -e DOCKER_GID=100 chbrandt/heasoft

This will run the image chbrandt/heasoft (which uses entrypoint.sh) as user brandt, that has uid=500 and gid=100.

/.\