Single init script for multiple containers?

[qwertyarpit]

Body

I'm running three containers from the same Docker image, but I only want an init script to run in one of them (like setting up a database, seeding data, etc.).

Right now, I can pass the script when running the container manually, but I’ve read that this isn't considered a best practice.

What’s the recommended way to ensure only one container runs the init logic, while the others skip it — without maintaining multiple images?

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[Keshavkumar04]

You can handle this by modifying your Docker image to include the init script via CMD or ENTRYPOINT, and using a custom environment variable like IS_MASTER to control whether the script runs.

🔧 Example Approach:

1. Add the init script to your image, and make your init script check for a flag:

# entrypoint.sh
if [ "$IS_MASTER" = "true" ]; then
  ./run-the-code
fi

2. Set the IS_MASTER env var when running just one container:

docker run -e IS_MASTER=true true your-image

And for the others:

docker run your-image

This way, you keep a single image but control behavior cleanly through environment variables.

[aryanorastar]

You can handle this using a single Docker image by wrapping your init logic in a script that checks an environment variable.

Steps:

1. Add an entrypoint.sh like this:

#!/bin/sh
if [ "$RUN_INIT" = "true" ]; then
  ./init.sh  # your DB setup or seeding script
fi

exec "$@"

2. In your Dockerfile, make sure this script is copied and used:

COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

3. Run your containers like this:

• For the one that runs init:

  docker run -e RUN_INIT=true your-image your-cmd

• For the others:

  docker run your-image your-cmd

✅ This way you keep a single image and just control behavior through environment variables — clean and scalable.