How to use an SSH key inside GitHub actions

Yesterday I moved the deployment for this site from a local script to GitHub actions. Overall it was a really pleasant experience because GitHub made it really easy to run scripts inside e.g. a Node.js environment, which I need to build the site.

One thing that was a bit tricky for me, was figuring out how to git push to my Dokku server from GitHub Actions. I needed to authenticate GitHub Actions for SSH access to my Dokku server.

I ended up generating a new SSH key for GitHub Actions and saving the private key to my repository's secrets (find them in the repo settings) as DOKKU_SSH_KEY.

Then I added a few lines to my main.yml file:

name: CI
on:
    push:
        branches: [master]
jobs:
    build:
        runs-on: ubuntu-latest
        steps:
            - uses: actions/checkout@v2
            - name: Setup Node.js environment
              uses: actions/setup-node@v1.4.2
              with:
                  node-version: 12.x
            - name: Add SSH key
              env:
                  SSH_AUTH_SOCK: /tmp/ssh_agent.sock
              run: |
                  mkdir -p /home/runner/.ssh
                  # Replace example.com with the hostname of the machine
                  # you're SSH-ing into
                  ssh-keyscan example.com >> /home/runner/.ssh/known_hosts
                  # DOKKU_SSH_KEY is the name of the repository secret
                  echo "${{ secrets.DOKKU_SSH_KEY }}" > /home/runner/.ssh/github_actions
                  chmod 600 /home/runner/.ssh/github_actions
                  ssh-agent -a $SSH_AUTH_SOCK > /dev/null   
                  ssh-add /home/runner/.ssh/github_actions
            - name: Install dependencies
              run: yarn
            - name: Build and deploy
              env:
                  SSH_AUTH_SOCK: /tmp/ssh_agent.sock
              run: |
                  git config --global user.email "actions@github.com"
                  git config --global user.name "GitHub actions"
                  yarn build --env production
                  git remote add dokku dokku@example.com:app-name
                  git add dist --force
                  git commit -m "Deploy"
                  git push dokku master -f

And that's all it took to get Github Actions authenticated with my Dokku server. I hope this was helpful to you, thanks for reading!