Containerizing cranc

How to run a docker container with the CLI app. First clone the repo:

git clone

cd cranc

Create a new dockerfile:

vim Dockerfile

Use for example the python:3-onbuild, as suggested in this guide. It is supposed to include some onbuild triggers, which for example COPY the requirements.txt file, RUN pip install on it and copy the current directory into /usr/src/app.

FROM python:3-onbuild

The next thing necessary is to install the app:

RUN python install

And finally to run the command (as entrypoint):


Time to make a build:

docker build -t cranc .

And run:

docker run cranc

Now it’s possible to run cranc in a container for example like this:

docker run cranc get issues

Docker starts the container, runs the command and exits the container. To avoid having to type docker run every time I want to run the cranc from a container, it is possible to create a bash script for example in user bin: /usr/bin/cranc with:


exec docker run -rm cranc "$@"

which means that every cranc command will add docker run before and append whatever comes after (“$@”).

Change it to executable:

chmod -x ~/bin/cranc

Don’t forget to source it:

source ~/bin/cranc

Like this, every time I write a cranc command, docker container will be started, command will run and container will exit. There is a way to avoid starting and exiting new container every time.

It is also possible to write a bash script which runs a docker container infinitely and the cranc commands can be faster, since there is no need to start a container with every command:


docker exec cranc cranc "$@"
if [ $rc -eq 1 ]; then
    docker run --entrypoint "sleep" --name cranc --detach cranc infinity
    docker exec cranc cranc "$@"

exit "$rc"

The script executes a docker container, that will run the commands - the bash and whatever follows. If it fails - the exit status equals to 1, that means that the container is not running ATM, then docker container will be ran from the sleep entrypoint (infinite sleep) and it will be detached (ran in the background). Then the docker exec cranc command will be ran again and the exit status will be returned.

Written on June 14, 2019