Using SSH keys with GitLab CI/CD (FREE)
GitLab currently doesn't have built-in support for managing SSH keys in a build environment (where the GitLab Runner runs).
Use SSH keys when you want to:
- Check out internal submodules.
- Download private packages using your package manager. For example, Bundler.
- Deploy your application to your own server or, for example, Heroku.
- Execute SSH commands from the build environment to a remote server.
- 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 that works
with any type of executor
(like Docker or shell, for example).
How it works
- Create a new SSH key pair locally with
- Add the private key as a variable to your project
- Run the
ssh-agentduring 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.
In the following example, the
ssh-add - command does not display the value of
$SSH_PRIVATE_KEY in the job log, though it could be exposed if you enable
debug logging. You might also want to
check the visibility of your pipelines.
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. In this case, you can use an SSH key pair.
You first must 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 CI/CD 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) ## - 'command -v ssh-agent >/dev/null || ( 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 - ## ## 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"
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 must 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, sign in to the server that runs your jobs.
Then, from the terminal, sign in 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 must add it as a deploy key.
After generating the key, try to sign in to the remote server 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. If anything suspicious happens, you notice it because the job fails (the SSH connection fails when the public keys don't 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 188.8.131.52
Create a new CI/CD variable with
SSH_KNOWN_HOSTS as "Key", and as a "Value" add the output of
If you must connect to multiple servers, all the server host keys must be collected in the Value of the variable, one key per line.
By using a 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 doesn't fail,
so there's something wrong with the server or the network.
Now that the
SSH_KNOWN_HOSTS variable is created, in addition to the
above, you must 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 susceptible 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'
We have set up an Example SSH Project for your convenience that runs on GitLab.com using our publicly available shared runners.
Want to hack on it? Fork it, commit, and push your changes. In a few moments the changes is picked by a public runner and the job starts.