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
• JENKINS_NAME: the name of the Jenkins agent

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

Create a cluster

    gcloud 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 container clusters get-credentials jenkins
kubectl config view --raw

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

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.

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

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

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

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

kubectl create -f ./src/main/kubernetes/jenkins-local.yml
kubectl create -f ./src/main/kubernetes/service.yml

More info

• Docker CookBook examples
• Kubernetes Getting started with Docker

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.

gcloud compute disks create --size 20GB kubernetes-jenkins

Creating the pods and services

kubectl create -f ./src/main/kubernetes/jenkins-gke.yml
kubectl create -f ./src/main/kubernetes/service-gke.yml

Connect to the ip of the network load balancer created by Kubernetes, port 80. Get the ip (in this case 104.197.19.100) with kubectl describe services/jenkins (it may take a bit to populate)

$ kubectl describe services/jenkins
Name:           jenkins
Namespace:      default
Labels:         <none>
Selector:       name=jenkins
Type:           LoadBalancer
IP:         10.175.244.232
LoadBalancer Ingress:   104.197.19.100
Port:           http    80/TCP
NodePort:       http    30080/TCP
Endpoints:      10.172.1.5:8080
Port:           slave   50000/TCP
NodePort:       slave   32081/TCP
Endpoints:      10.172.1.5:50000
Session Affinity:   None
No events.

Until Kubernetes 1.4 removes the SNATing of source ips, seems that CSRF (enabled by default in Jenkins 2) needs to be configured to avoid WARNING: No valid crumb was included in request errors. This can be done checking Enable proxy compatibility under Manage Jenkins -> Configure Global Security

Configure Jenkins, adding the Kubernetes cloud under configuration, setting Kubernetes URL to the container engine cluster endpoint or simply https://kubernetes.default.svc.cluster.local. Under credentials, click Add and select Kubernetes Service Account, or alternatively use the Kubernetes API username and password. Select 'Certificate' as credentials type if the kubernetes cluster is configured to use client certificates for authentication.

You may want to set Jenkins URL to the internal service IP, http://10.175.244.232 in this case, to connect through the internal network.

Set Container Cap to a reasonable number for tests, i.e. 3.

Add an image with

• Docker image: jenkinsci/jnlp-slave
• Jenkins slave root directory: /home/jenkins

Now it is ready to be used.

Tearing it down

kubectl stop rc/jenkins
kubectl delete services/jenkins

docker build -t csanchez/jenkins-kubernetes .