Adding an SSH Key to CircleCI

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Cloud Server v3.x Server v2.x

If deploying to your servers requires SSH access, you will need to add SSH keys to CircleCI.

Overview

There are two reasons to add SSH keys to CircleCI:

1. To check out code from version control systems.
2. To enable running processes to access other services.

If you are adding an SSH key for the first reason, refer to the GitHub and Bitbucket Integration document.

Otherwise, follow the steps below for the version of CircleCI you are using to add an SSH key to your project.

Note: You may need to add the public key to ~/.ssh/authorized_keys in order to add SSH keys.

Steps

Note: Since CircleCI cannot decrypt SSH keys, every new key must have an empty passphrase.

CircleCI cloud or server 3.x

1. In a terminal, generate the key with ssh-keygen -t ed25519 -C "your_email@example.com". See Secure Shell documentation for additional details.

2. In the CircleCI application, go to your project’s settings by clicking the the Project Settings button (top-right on the Pipelines page of the project).

3. On the Project Settings page, click on SSH Keys (vertical menu on the left).

4. Scroll down to the Additional SSH Keys section.

5. Click the Add SSH Key button.

6. In the Hostname field, enter the key’s associated host (for example, git.heroku.com). If you do not specify a hostname, the key will be used for all hosts.

7. In the Private Key field, paste the SSH key you are adding.

8. Click the Add SSH Key button.

CircleCI server 2.19.x

1. In a terminal, generate the key with ssh-keygen -m PEM -t rsa -C "your_email@example.com". See the (SSH) Secure Shell documentation web site for additional details.

2. In the CircleCI application, go to your project’s settings by clicking the gear icon next to your project.

3. In the Permissions section, click on SSH Permissions.

4. Click the Add SSH Key button.

5. In the Hostname field, enter the key’s associated host (for example, “git.heroku.com”). If you do not specify a hostname, the key will be used for all hosts.

6. In the Private Key field, paste the SSH key you are adding.

7. Click the Add SSH Key button.

Adding SSH Keys to a Job

Even though all CircleCI jobs use ssh-agent to automatically sign all added SSH keys, you must use the add_ssh_keys key to actually add keys to a container.

To add a set of SSH keys to a container, use the add_ssh_keys special step within the appropriate job in your configuration file.

For a self-hosted runner, ensure that you have an ssh-agent on your system to successfully use the add_ssh_keys step. The SSH key is written to $HOME/.ssh/id_rsa_<fingerprint>, where $HOME is the home directory of the user configured to execute jobs, and <fingerprint> is the fingerprint of the key. A host entry is also appended to $HOME/.ssh/config, along with a relevant IdentityFile option to use the key.

version: 2
jobs:
  deploy-job:
    steps:
      - add_ssh_keys:
          fingerprints:
            - "SO:ME:FIN:G:ER:PR:IN:T"

Note: All fingerprints in the fingerprints list must correspond to keys that have been added through the CircleCI application.

Adding multiple keys with blank hostnames

If you need to add multiple SSH keys with blank hostnames to your project, you will need to make some changes to the default SSH configuration provided by CircleCI. In the scenario where you have multiple SSH keys that have access to the same hosts, but are for different purposes the default IdentitiesOnly no is set causing connections to use ssh-agent. This will always cause the first key to be used, even if that is the incorrect key. If you have added the SSH key to a container, you will need to either set IdentitiesOnly no in the appropriate block, or you can remove all keys from the ssh-agent for this job using ssh-add -D, and reading the key added with ssh-add /path/to/key.

See Also

GitHub and Bitbucket Integration

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