Using SSH keys with GitLab CI/CD
GitLab currently doesn't have built-in support for managing SSH keys in a build environment (where the GitLab Runner runs).
The SSH keys can be useful when:
- You want to checkout internal submodules
- You want to download private packages using your package manager (e.g., Bundler)
- You want to deploy your application to your own server, or, for example, Heroku
- You want to execute SSH commands from the build environment to a remote server
- You want to rsync files from the build environment to a remote server
If anything of the above rings a bell, then you most likely need an SSH key.
The most widely supported method is to inject an SSH key into your build
environment by extending your
.gitlab-ci.yml, and it's a solution which works
with any type of executor
(Docker, shell, etc.).
How it works
- Create a new SSH key pair locally with ssh-keygen
- Add the private key as a secret variable to your project
- Run the ssh-agent during job to load the private key.
- Copy the public key to the servers you want to have access to (usually in
~/.ssh/authorized_keys) or add it as a deploy key if you are accessing a private GitLab repository.
SSH keys when using the Docker executor
When your CI/CD jobs run inside Docker containers (meaning the environment is contained) and you want to deploy your code in a private server, you need a way to access it. This is where an SSH key pair comes in handy.
You will first need to create an SSH key pair. For more information, follow the instructions to generate an SSH key. Do not add a passphrase to the SSH key, or the
before_scriptwill\ prompt for it.
Create a new secret variable. As Key enter the name
SSH_PRIVATE_KEYand in the Value field paste the content of your private key that you created earlier.
before_scriptaction. In the following example, a Debian based image is assumed. Edit to your needs:
before_script: ## ## Install ssh-agent if not already installed, it is required by Docker. ## (change apt-get to yum if you use an RPM-based image) ## - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )' ## ## Run ssh-agent (inside the build environment) ## - eval $(ssh-agent -s) ## ## Add the SSH key stored in SSH_PRIVATE_KEY variable to the agent store ## We're using tr to fix line endings which makes ed25519 keys work ## without extra base64 encoding. ## https://gitlab.com/gitlab-examples/ssh-private-key/issues/1#note_48526556 ## - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add - > /dev/null ## ## Create the SSH directory and give it the right permissions ## - mkdir -p ~/.ssh - chmod 700 ~/.ssh ## ## Optionally, if you will be using any Git commands, set the user name and ## and email. ## #- git config --global user.email "email@example.com" #- git config --global user.name "User name"
NOTE: Note: The
before_scriptcan be set globally or per-job.
Make sure the private server's SSH host keys are verified.
As a final step, add the public key from the one you created in the first step to the services that you want to have an access to from within the build environment. If you are accessing a private GitLab repository you need to add it as a deploy key.
That's it! You can now have access to private servers or repositories in your build environment.
SSH keys when using the Shell executor
If you are using the Shell executor and not Docker, it is easier to set up an SSH key.
You can generate the SSH key from the machine that GitLab Runner is installed on, and use that key for all projects that are run on this machine.
First, you need to login to the server that runs your jobs.
Then from the terminal login as the
sudo su - gitlab-runner
Generate the SSH key pair as described in the instructions to generate an SSH key. Do not add a passphrase to the SSH key, or the
before_scriptwill prompt for it.
As a final step, add the public key from the one you created earlier to the services that you want to have an access to from within the build environment. If you are accessing a private GitLab repository you need to add it as a deploy key.
Once done, try to login to the remote server in order to accept the fingerprint:
For accessing repositories on GitLab.com, you would use
Verifying the SSH host keys
It is a good practice to check the private server's own public key to make sure you are not being targeted by a man-in-the-middle attack. In case anything suspicious happens, you will notice it since the job would fail (the SSH connection would fail if the public keys would not match).
To find out the host keys of your server, run the
ssh-keyscan command from a
trusted network (ideally, from the private server itself):
## Use the domain name ssh-keyscan example.com ## Or use an IP ssh-keyscan 18.104.22.168
Create a new secret variable with
SSH_KNOWN_HOSTS as "Key", and as a "Value" add the output of
NOTE: Note: If you need to connect to multiple servers, all the server host keys need to be collected in the Value of the variable, one key per line.
By using a secret variable instead of
ssh-keyscan directly inside
.gitlab-ci.yml, it has the benefit that you don't have to change
if the host domain name changes for some reason. Also, the values are predefined
by you, meaning that if the host keys suddenly change, the CI/CD job will fail,
and you'll know there's something wrong with the server or the network.
Now that the
SSH_KNOWN_HOSTS variable is created, in addition to the
above, here's what more you need to add:
before_script: ## ## Assuming you created the SSH_KNOWN_HOSTS variable, uncomment the ## following two lines. ## - echo "$SSH_KNOWN_HOSTS" > ~/.ssh/known_hosts' - chmod 644 ~/.ssh/known_hosts ## ## Alternatively, use ssh-keyscan to scan the keys of your private server. ## Replace example.com with your private server's domain name. Repeat that ## command if you have more than one server to connect to. ## #- ssh-keyscan example.com >> ~/.ssh/known_hosts #- chmod 644 ~/.ssh/known_hosts ## ## You can optionally disable host key checking. Be aware that by adding that ## you are suspectible to man-in-the-middle attacks. ## WARNING: Use this only with the Docker executor, if you use it with shell ## you will overwrite your user's SSH config. ## #- '[[ -f /.dockerenv ]] && echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config'
Want to hack on it? Simply fork it, commit and push your changes. Within a few moments the changes will be picked by a public runner and the job will begin.