Startup script for a docker container

Question

I have a docker container already running. I have made some configuration changes, let's say have added some host info in /etc/hosts inside the container. How do I keep the changes saved, so that next time when I open an interactive shell to the container I don't have to do the same stuff again ? For now I have created a mini script as addhosts.sh as below inside the container and have to run it every time.

echo "1.2.3.4 server1.example.com gluster1" >> /etc/hosts
echo "5.6.7.8 server2.example.com gluster2" >> /etc/hosts

This is one of the cases. Similarly, I need all my configuration to be intact. Please don't suggest for dockerfile as I'm not creating an image rather I'm just getting into the container.

Answer 1

You can commit the changes you made by:

Short Command reference:

docker commit <container id or name>  <repository name>/<your image name>:<tage aka version>

Example:

docker commit c3f279d17e0a  svendowideit/testimage:version3

Full Reference:

Usage:  docker commit [OPTIONS] CONTAINER [REPOSITORY[:TAG]]

Create a new image from a container's changes

Options:
  -a, --author string    Author (e.g., "John Hannibal Smith <[email protected]>")
  -c, --change value     Apply Dockerfile instruction to the created image (default [])
      --help             Print usage
  -m, --message string   Commit message
  -p, --pause            Pause container during commit (default true)

Then you can use docker images to view your new Image after commit.

To run a container from your new Image:

docker run -d svendowideit/testimage:version3 <optional startup command>

Another way would be creating your own image via: dockerfile, I'm Just putting it here just incase we can help others.

Answer 2

Assuming you do not wish to save the changes into a new image:

docker exec -it container_id echo "1.2.3.4 server1.example.com gluster1" >> /etc/hosts
docker exec -it container_id echo "5.6.7.8 server2.example.com gluster2" >> /etc/hosts

That would connect to the container, run the command and exit without killing the container.

Notice the difference between the following:

docker exec -it container_id ... = does not kill the container. 
docker run -it container_id   ...= kills the container