How to copy a file to a Docker container before starting/running it?

Question

I'm starting with a docker image that is already built. I would like to do this

1. Create a docker container from this image. (Don't start)
2. Copy a file to this container
3. Start the container

How can this be achieved. It looks like if i run the following commands the file doesn't end up in the container

1. docker create --name my_container my_image
2. docker cp file my_container:/tmp/file
3. docker start my_container

Any idea how this can be achieved ?

Answer 1

You will have to create a new image from a Dockerfile that inherit from the one that is already built, and the use the COPY tag:

Dockerfile

FROM my_image
COPY file /tmp/file

Finally, build that new Dockerfile:

$ docker build -t new_image .