Install SSH Key

This action installs SSH key in ~/.ssh.

Useful for SCP, SFTP, and rsync over SSH in deployment script.

tested on:

• all available virtual machines (Windows Server 2022/2019, macOS Monterey/Big Sur, and Ubuntu 22.04/20.04)
• Docker container (Ubuntu) / requires openssh-client package; apt install -y openssh-client
• Docker container (CentOS) / requires openssh-clients package; yum install -y openssh-clients
• Docker container (Alpine Linux) / requires openssh-client package; apk add openssh-client

Usage

Add your SSH key to your product secrets by clicking Settings - Secrets - Add a new secret beforehand.

PEM(RSA), PKCS8, and RFC4716(OpenSSH) formats are OK.

runs-on: ubuntu-latest
steps:
- name: Install SSH key
  uses: niaid/monarch-actions-key-writer@v2
  with:
    key: ${{ secrets.SSH_KEY }}
    name: id_rsa # optional
    known_hosts: ${{ secrets.KNOWN_HOSTS }}
    config: ${{ secrets.CONFIG }} # ssh_config; optional
    if_key_exists: fail # replace / ignore / fail; optional (defaults to fail)
- name: rsync over SSH
  run: rsync -r ./foo/ user@remote:bar/

See Workflow syntax for GitHub Actions for details.

NOTE:

• Server key of github.com will be always set to known_hosts.
• SSH keys will be removed at the end of workflow.

Install multiple keys

If you want to install multiple keys, call this action multiple times. It is useful for port forwarding.

NOTE: When this action is called multiple times, the contents of known_hosts and config will be appended. key must be saved as different name, by using name option.

runs-on: ubuntu-latest
steps:
- name: Install SSH key of bastion
  uses: niaid/monarch-actions-key-writer@v2
  with:
    key: ${{ secrets.SSH_KEY_OF_BASTION }}
    name: id_rsa-bastion
    known_hosts: ${{ secrets.KNOWN_HOSTS_OF_BASTION }}
    config: |
      Host bastion
        HostName xxx.xxx.xxx.xxx
        User user-of-bastion
        IdentityFile ~/.ssh/id_rsa-bastion
- name: Install SSH key of target
  uses: niaid/monarch-actions-key-writer@v2
  with:
    key: ${{ secrets.SSH_KEY_OF_TARGET }}
    name: id_rsa-target
    known_hosts: ${{ secrets.KNOWN_HOSTS_OF_TARGET }} # will be appended to existing .ssh/known_hosts
    config: |                                         # will be appended to existing .ssh/config
      Host target
        HostName yyy.yyy.yyy.yyy
        User user-of-target
        IdentityFile ~/.ssh/id_rsa-target
        ProxyCommand ssh -W %h:%p bastion
- name: SCP via port-forwarding
  run: scp ./foo/ target:bar/

Q&A

SSH failed even though key has been installed.

Check below:

• Host key verification failed.:
  • Set known_hosts parameter correctly (use ssh-keyscan command).

I want to replace/ignore key if exists.

Use if_key_exists parameter.

• replace: replaces key
• ignore: does nothing
• fail: fails (default)

How do I use encrypted SSH key?

This action doesn't support encrypted key directly. Here are some solutions:

• decrypting key beforehand: best bet, and works on any VM
• sshpass command: next best bet, but not supported on Windows
• expect command: be careful not to expose passphrase to console
• SSH_ASKPASS environment variable: might be troublesome

Which one is the best way for transferring files, "direct SCP/SFTP/rsync" or "SCP/SFTP/rsync via bastion"?

I recommend rsync via bastion.

rsync -r -e "ssh bastion ssh" ./foo/ target:bar/

It has some advantages over other methods:

• "Rsync via bastion" doesn't require to update workflow files and secrets even if it is necessary to transfer files to multiple servers.
  • Other methods require to update known_hosts if servers have changed.
• Rsync:
  • is fastest of all.
  • does NOT break files even if disconnected during transferring.
  • can remove files that don't exist on server.
• SCP is deprecated by OpenSSH due to outdated and inflexible protocol.
• Using bastion is more secure because:
  • it is not necessarily to expose SSH port on servers to public.
    • Address filtering is less effective.
    • Because Azure address range is very wide.
    • And will be updated continuously.
  • if security incident ―e.g., private key leaked― occurs, it's OK just to remove authorized_keys on bastion.

I want to omit known_hosts.

First of all, you have to understand that it is NOT secure to SSH with no known_hosts and using StrictHostKeyChecking=no option.

Why do you want to omit it? If the reason is "I'm not understanding about the function of known_hosts" or "It's bother to fetch server key", you should not omit. If "It is hard to prefetch server key because the server will be created dynamically", you can use bastion server.

"known_hosts is unnecessary because I'm using secure method for SSH, such as SSHFP and signed server key." — OK, here is a special value to omit known_hosts. You should use it ONLY IF you are using secure methods... It is known_hosts: unnecessary.

License

The scripts and documentation in this project are released under the MIT License

Changelog

See CHANGELOG.md.