Htykuut

Is it possible to run a python script automatically upon starting a Docker container?

My command to attach to an image is:

docker run -i -t --entrypoint /bin/bash myimage -s

Is there a way to add an additional command that runs a script upon launching it?
I would prefer not to use a Dockerfile as some of the python modules I use are from private repos and need to be downloaded manually, so a Dockerfile would not completely build the image I want.

As a matter of fact there is. Just don't use --entrypoint. Instead:

docker run -it myimage /bin/bash -c /run.sh

Obviously, this assumes that the image itself contains a simple Bash script at the location /run.sh.

#!/bin/bash

command1

command2

command3

...

If you don't want that, you can mount the current folder inside the running container and run a local script:

docker run -it -v $(pwd):/mnt myimage /bin/bash -c /mnt/run.sh

ENTRYPOINT vs. CMD seems to be a common cause of confusion.

Think about it this way:

• 
  ENTRYPOINT is a way to hard-code a certain behavior that cannot be changed after setting it up.


• 
  CMD is the default way to supply a command to be run.

Docker containers can be set up to run as self-contained applications. If you're so inclined, you could create throwaway containers that accept command line arguments (a file for example), pull that in, work their magic and return you a processed file. Some people use this to set up build environments with different configurations and just run them on demand, not cluttering up their host machine.

However, your usage scenario feels tedious, since you are apparently doing the setup by hand. It would be easier to set the download credentials as environment variables, like this:

docker run -d -e "DEEP=purple" -e "LED=zeppelin" myimage /bin/bash -c /run.sh

You can then use those within the script as placeholders. This way, you get the best of both worlds. For added security, your run.sh should unset the environment variables once they have been used, like this:

#!/bin/bash

command1

command2

command3

...

unset DEEP

unset LED