Copy files between two docker containers using scp

Question

I have created two docker containers named as server and client using alpine image and I am running both containers. Then I installed apk add openssh and apk add openrc in both the containers. Using rc-service sshd start I have started the ssh service. Now, I want to copy a file using scp.

From server container I typed:

scp myfile.txt [email protected]:/location_of_the_folder

It is asking a password for the client container. What can I do? What is the default password for docker container(s)?

I have tried 3 options as follows:

1. Attach the same volume to both the containers.
2. Using docker cp from server container to host and then host to client container.
3. Using ssh-keygen in the server container and copied the id_rsa.pub key manually to client containers /root/.ssh directory and it works.

I don't want to use options 1 and 2. What should I do for option 3 using shell script? I want to automate this thing. I can do it manually, but can we do it by automation using a shell script, to copy some text from one container to another container?

Answer 1

If it's a local docker container, use docker cp as explained here:

docker cp {container_name}:{file_path} {target_file_path OR target_dir_ended_with_slash}

But if you really need ssh (e.g. when container runs in a remote host), try these steps:

1. Make sure you run your container with ssh port 22 redirection from host, e.g. docker run -p 8022:22 ...

Then inside the container:

2. Install sshd: sudo apt update && sudo apt install -y openssh-server

3. Create sshd directory: mkdir /var/run/sshd

4. Add password to current user ("root" user doesn't have password by default): passwd

5. Set PermitRootLogin yes in sshd_config: sudo sed -i 's/PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config

6. You might also need: sudo sed 's@session\s*required\s*pam_loginuid.so@session optional pam_loginuid.so@g' -i /etc/pam.d/sshd

7. And: sudo sh -c 'echo "export VISIBLE=now" >> /etc/profile'

8. Restart sshd service: sudo service ssh restart

Then you should be able to connect with SSH, and transfer files with SCP.

If you get "port 22: Connection refused", try any of these workarounds:

• Run container with privileged access: docker exec --privileged -ti container_name bash
• Inside container, open port 22 with UFW firewall: sudo apt-get install -y ufw && sudo ufw allow 22