Run command in Docker Container only on the first start

Question

I have a Docker Image which uses a Script (/bin/bash /init.sh) as Entrypoint. I would like to execute this script only on the first start of a container. It should be omitted when the containers is restarted or started again after a crash of the docker daemon.

Is there any way to do this with docker itself, or do if have to implement some kind of check in the script?

question from:https://stackoverflow.com/questions/37836764/run-command-in-docker-container-only-on-the-first-start

Answer 1

I had the same issue, here a simple procedure (i.e. workaround) to solve it:

Step 1:

Create a "myStartupScript.sh" script that contains this code:

CONTAINER_ALREADY_STARTED="CONTAINER_ALREADY_STARTED_PLACEHOLDER"
if [ ! -e $CONTAINER_ALREADY_STARTED ]; then
    touch $CONTAINER_ALREADY_STARTED
    echo "-- First container startup --"
    # YOUR_JUST_ONCE_LOGIC_HERE
else
    echo "-- Not first container startup --"
fi

Step 2:

Replace the line "# YOUR_JUST_ONCE_LOGIC_HERE" with the code you want to be executed only the first time the container is started

Step 3:

Set the scritpt as entrypoint of your Dockerfile:

ENTRYPOINT ["/myStartupScript.sh"]

In summary, the logic is quite simple, it checks if a specific file is present in the filesystem; if not, it creates it and executes your just-once code. The next time you start your container the file is in the filesystem so the code is not executed.