Jenkins SSH Agent Docker Image

Docker image for Jenkins agents connected over SSH

A https://jenkins.io agent image which allows using SSH to establish the connection. It can be used together with the https://plugins.jenkins.io/ssh-slaves or other similar plugins.

See https://wiki.jenkins-ci.org/display/JENKINS/Distributed+builds for more info.

Running

Running with the SSH Build Agents plugin

To run a Docker container

bash
docker run -d --rm --name=agent --publish 2200:22 -e "JENKINS_AGENT_SSH_PUBKEY=<public_key>" jenkins/ssh-agent

• -d: To start a container in detached mode, use the -d option. Containers started in detached mode exit when the root process used to run the container exits, unless you also specify the --rm option.
• --rm: If you use -d with --rm, the container is removed when it exits or when the daemon exits, whichever happens first.
• --name: Assigns a name to the container. If you do not specify a name, Docker generates a random name.
• --publish 2200:22: Publishes the host port 2200 to the agent container port 22 (SSH) to allow connection from the host with ssh jenkins@localhost -p 2200

Please note none of these options are mandatory, they are just examples.

You will then be able to connect this agent using the https://plugins.jenkins.io/ssh-slaves as "jenkins" with the matching private key.

When using the Linux image, you have to set the value of the Remote root directory to /home/jenkins/agent in the agent configuration UI.

When using the Windows image, you have to set the value of the Remote root directory to C:/Users/jenkins/Work in the agent configuration UI.

If you intend to use another directory than /home/jenkins/agent under Linux or C:/Users/jenkins/Work under Windows, don't forget to add it as a data volume.

bash
docker run -v docker-volume-for-jenkins-ssh-agent:/home/jenkins/agent:rw jenkins/ssh-agent "<public key>"

How to use this image with Docker Plugin

To use this image with https://plugins.jenkins.io/docker-plugin, you need to pass the public SSH key using environment variable JENKINS_AGENT_SSH_PUBKEY and not as a startup argument.

In Environment field of the Docker Template (advanced section), just add:

JENKINS_AGENT_SSH_PUBKEY=<YOUR PUBLIC SSH KEY HERE>

Don't put quotes around the public key.

Please note that you have to set the value of the Remote File System Root to /home/jenkins/agent in the Docker Agent Template configuration UI.

If you intend to use another directory than /home/jenkins/agent, don't forget to add it as a data volume.

You should be all set.

Extending the image

Should you need to extend the image, you could use something along those lines:

Dockerfile
FROM jenkins/ssh-agent:debian-jdk17 as ssh-agent
# [...]
COPY --chown=jenkins mykey "${JENKINS_AGENT_HOME}"/.ssh/mykey
# [...]

Configurations

The image has several supported configurations, which can be accessed via the following tags:

${IMAGE_VERSION} can be found on the https://github.com/jenkinsci/docker-ssh-agent/releases page.

• latest, latest-jdk11, jdk11, latest-bullseye-jdk11, bullseye-jdk11, latest-debian-jdk11, debian-jdk11, ${IMAGE_VERSION}, ${IMAGE_VERSION}-jdk11, (Dockerfile)
• latest-jdk17, jdk17, latest-bullseye-jdk17, bullseye-jdk17,latest-debian-jdk17, debian-jdk17, ${IMAGE_VERSION}-jdk17, (Dockerfile)
• nanoserver-1809, nanoserver-ltsc2019, nanoserver-1809-jdk11, nanoserver-ltsc2019-jdk11, ${IMAGE_VERSION}-nanoserver-1809, ${IMAGE_VERSION}-nanoserver-ltsc2019, ${IMAGE_VERSION}-nanoserver-1809-jdk11, ${IMAGE_VERSION}-nanoserver-ltsc2019-jdk11 (Dockerfile)
• windowsservercore-1809, windowsservercore-ltsc2019, windowsservercore-1809-jdk11, windowsservercore-ltsc2019-jdk11, ${IMAGE_VERSION}-windowsservercore-1809, ${IMAGE_VERSION}-windowsservercore-ltsc2019, ${IMAGE_VERSION}-windowsservercore-1809-jdk11, ${IMAGE_VERSION}-windowsservercore-ltsc2019-jdk11 (Dockerfile)

Building instructions

Pre-requisites

Should you want to build this image on your machine (before submitting a pull request for example), please have a look at the pre-requisites:

• A GNU/Linux machine with https://docs.docker.com/engine/install/, a macOS machine with https://docs.docker.com/desktop/install/mac-install/, or a Windows machine with https://docs.docker.com/docker-for-windows/ installed
• Docker BuildX plugin https://github.com/docker/buildx#installing on older versions of Docker (from 19.03). Docker Buildx is included in recent versions of Docker Desktop for Windows, macOS, and Linux. Docker Linux packages also include Docker Buildx when installed using the DEB or RPM packages.
• https://www.gnu.org/software/make/ installed
• jq installed
• https://www.gnu.org/software/bash/ installed
• git installed
• curl installed

Building

Target images

If you want to see the target images that will be built, you can issue the following command:

bash
make list
alpine_jdk11
alpine_jdk17
debian_jdk11
debian_jdk17

Building a specific image

If you want to build a specific image, you can issue the following command:

bash
make build-<OS>_<JDK_VERSION>

That would give for JDK 11 on Alpine Linux:

bash
make test-alpine_jdk11

Building all images

Then, you can build all the images by running:

bash
make build

Testing all images

If you want to test the images, you can run:

bash
make test

Testing a specific image

If you want to test a specific image, you can run:

bash
make test-<OS>_<JDK_VERSION>

That would give for JDK 11 on Alpine Linux:

bash
make test-alpine_jdk11

Other make targets

show gives us a detailed view of the images that will be built, with the tags, platforms, and Dockerfiles.

bash
make show
{
  "group": {
    "default": {
      "targets": [
        "alpine_jdk17",
        "alpine_jdk11",
        "debian_jdk11",
        "debian_jdk17"
      ]
    }
  },
  "target": {
    "alpine_jdk11": {
      "context": ".",
      "dockerfile": "alpine/Dockerfile",
      "tags": [
        "docker.io/jenkins/ssh-agent:alpine-jdk11",
        "docker.io/jenkins/ssh-agent:latest-alpine-jdk11"
      ],
      "platforms": [
        "linux/amd64"
      ],
      "output": [
        "type=docker"
      ]
    },
    [...]

bats is a dependency target. It will update the https://github.com/bats-core/bats-core and run the tests.

bash
make bats
make: 'bats' is up to date.

Changelog

See https://github.com/jenkinsci/docker-ssh-agent/releases/latest. Note that the changelogs and release tags were introduced in Dec 2019, and there are no entries for previous releases. Please consult with the commit history if needed.