elibixby / kubernetes-plugin

Jenkins plugin to run dynamic slaves in a Kubernetes/Docker environment

jenkins-kubernetes-plugin

Jenkins plugin to run dynamic slaves in a Kubernetes/Docker environment.

Based on the Scaling Docker with Kubernetes article, automates the scaling of Jenkins slaves running in Kubernetes.

The plugin creates a Kubernetes Pod for each slave started, defined by the Docker image to run, and stops it after each build.

Slaves are launched using JNLP, so it is expected that the image connects automatically to the Jenkins master. For that some environment variables are automatically injected:

• JENKINS_URL: Jenkins web interface url
• JENKINS_JNLP_URL: url for the jnlp definition of the specific slave
• JENKINS_SECRET: the secret key for authentication

Tested with csanchez/jenkins-slave, see the Docker image source code.

Configuration on Google Container Engine

Create a cluster

    gcloud beta container clusters create jenkins --num-nodes 1 --machine-type g1-small

and note the admin password and server certitifate.

Or use Google Developer Console to create a Container Engine cluster, then run

    gcloud beta container get-credentials
    kubectl config view --raw

the last command will output kubernetes cluster configuration including API server URL, admin password and root certificate

Debugging

To inspect the json messages sent back and forth to the Kubernetes API server you can configure a new Jenkins log recorder for org.apache.http at DEBUG level.

Building

Run mvn clean package and copy target/kubernetes.hpi to Jenkins plugins folder.

Docker image

Docker image for Jenkins, with plugin installed. Based on the official image.

Running

docker run --rm --name jenkins -p 8080:8080 -p 50000:50000 -v /var/jenkins_home csanchez/jenkins-kubernetes

Testing locally

A local testing cluster with one node can be created with Docker Compose

docker-compose up

When using boot2docker or Docker Engine with a remote host, the remote Kubernetes API can be exposed with docker-machine ssh MACHINE_NAME -- -L 0.0.0.0:8080:localhost:8080 or boot2docker ssh -L 0.0.0.0:8080:localhost:8080

More info

• Docker CookBook examples
• Kubernetes Getting started with Docker

Running in Kubernetes (Google Container Engine)

Assuming you created a Kubernetes cluster named jenkins this is how to run both Jenkins and slaves there.

Create a GCE disk named kubernetes-jenkins to store the data, and format it as ext4. Formatting is not needed in new versions of Kubernetes.

Creating the pods and services

gcloud preview container pods create --config-file ./src/main/kubernetes/pod.yml
gcloud preview container services create --config-file ./src/main/kubernetes/service-http.yml
gcloud preview container services create --config-file ./src/main/kubernetes/service-slave.yml

Open the firewall to the Jenkins master running in a pod

gcloud compute firewall-rules create jenkins-node-master --allow=tcp:8888 --target-tags k8s-jenkins-node

Connect to the ip of the network load balancer created by Kubernetes, port 8888. Get the ip with

gcloud compute forwarding-rules describe jenkins

Configure Jenkins, adding the Kubernetes cloud under configuration, setting Kubernetes URL to the container engine cluster endpoint, and the correct username and password. Set Container Cap to a reasonable number for tests, i.e. 3.

Add an image with

• ID: csanchez/jenkins-slave
• Remote filesystem root: /home/jenkins
• Remote FS Root Mapping: /home/jenkins

Now it is ready to be used.

Tearing it down

gcloud preview container pods delete jenkins
gcloud preview container services delete jenkins
gcloud preview container services delete jenkins-slave

Building

docker build -t csanchez/jenkins-kubernetes .