SSH keys for Docker executor

Question

I have created an image where I run some tasks.
I want to be able to push some files to a remote server that runs Windows Server 2022.

The gitlab-runner runs on an Ubuntu machine.
I managed to do that using shell executors. But now I want to do the same inside a docker container.

Using the following guide
https://docs.gitlab.com/ee/ci/ssh_keys/#ssh-keys-when-using-the-docker-executor
I don't understand in which user I will create the keys.

In a shell executor case I used gitlab-runner user in which I created a pair of keys. I added the public key to the server that I want to push files to and it worked.

However, I added the same private key into the gitlab CI/CD variable as the guide suggests.
Then inside the job I added the following:

  before_script:
    - 'command -v ssh-agent >/dev/null || ( apt-get update -y && apt-get install openssh-client -y )'
    - eval $(ssh-agent -s)
    - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add -
    - mkdir -p ~/.ssh
    - chmod 700 ~/.ssh
  script:
    - scp -P <port> myfile.txt username@ip:remote_path

But the job fails with errors

Host key verification failed.
lost connection

Should I use the same private key from gitlab-runner user?

PS: The echo "$SSH_PRIVATE_KEY" works. I can see the key I added in the gitlab CI/CD variable.

Answer 1

I used something similar in my CI process, works like a charm, I recall I've used some base64 formatted runner key due to some formatting errors:

- echo $GITLAB_RUNNER_SSH_KEY | base64 -d > $HOME/.ssh/runner_key
- chmod -R 600 ~/.ssh
- eval $(ssh-agent -s)
- ssh-add $HOME/.ssh/runner_key