John Storey

Jenkins, Hugo, and Docker

Wow, it's been a fun, exciting time. My new job has curtailed my machine learning studies (with day work and night calls to a time zone thirteen hours away taking up my time.) Mostly I get a few hours in on Saturday mornings right now. Hopefully early February my schedule will free up a bit though.

Jenkins Deployment of This Blog

One of my current efforts is to understand enough of what our dev ops engineer has set up so that I can be a backup if there is an emergency while he is on vacation. He's setting up a great CI system using

  • Jenkins
  • Docker
  • Kubernetes

These are all technologies I was somewhat familiar with, but I've been having to learn alot more. Along the way I thought it would be fun to move this blog deployment to a local Jenkins running on my laptop.

Here is how I am currently deploying this blog to the cloud:

  • Check new posts into a git repository. I use the Hugo static site generator, so that is the repository layout.
  • Manually run a Jenkins pipeline job, with Jenkins running in a Docker container.
  • The pipeline starts a build agent in another Docker container on the host.
  • It checks out the blog from the git repository and generates the static site.
  • SSH is used to deploy the newly generated blog to production, where it's now readable by you!

Out of all this, the new challenge for me was determining the correct way to pass the SSH key into the build agent. This is what I did.

SSHAgent Plugin

It turns out that is rather easy. You can install the Jenkins plugin SSH Agent, which will pass Jenkins credentials from Jenkins into build agents. This is a pipeline compatiable plugin, and works great with private SSH keys. Here is how you use it.

TODO Setup the SSH Credentials

Jenkins allows you to set a Credential in different scopes. It can be scoped globally, or restricted to a folder and below. I clicked the sidebar menu item Credentials to create a Credential of type "SSH key with username". Here are the values I filled in. Yes, I have hidden most of my private key -- what would you need that for?

Credential creation screen

Notice two interesting field choices here

  • Username: jenkins
  • ID: personal-blog

The username should usually be "jenkins". I thought it would be the user for SSH, but when we look at the pipeline you'll see that's not needed.

If you leave it blank, the ID will be auto-generated. I'm deploying a personal blog, and have chose to name my credentials "personal-blog" instead of having a randomly generated value.

Notice that while the scope of the Credential can be limited to a folder, I happen to be using a global scope here. That's not exactly best practice and you should not follow my example.

Lastly be aware that you are pasting in the private key you want to use, not the public one.

Usin the SSH Credentials in the Build Agent

As I mentioned, my build agent is also a container. We need a way, via the pipeline, to pass in the credentials we just created before we use our SSH key.

Remember the ID we set -- "personal-blog"? Install the SSHAgent Jenkins plugin, and you can wrap your SSH commands in the pipeline. Here is my "Deploy" step where I use it.

stage('Deploy') {
  steps {
    sshagent(['personal-blog']) {
      sh "ssh -o StrictHostKeyChecking=no 'rm -rf /var/www/html/*' "
      sh 'scp -r public/* '

Notice that I reference the Credential ID "personal-blog" here. By using the ID, the wrapped SSH commands will automatically use the referenced private key.

Yes, I know this code is not the most advanced deployment strategy. It's just my blog though -- blue / green deployment is probably overkill. (Okay, maybe a Jenkins pipeline is overkill as well, but hey! pipelines! cool!!!!!).


  • Install the SSHAgent plugin for Jenkins.
  • Create SSH with Username credentials.
  • Use the sshagent command in pipelines to reference the credentials by ID.