Docker Containers as Jenkins Slaves

A friend of mine asked me to try to attach Slave nodes to Jenkins Master. And Yes, it is straigthforward in jenkins, you just need to go to :

Manage Jenkins -> Manage Nodes -> Add Node

Some basic configuration and you’re DONE.
But the interesting part of this is, he wants these slaves to be docker containers. (This is Interesting =D ).

I don’t know if my method is the best way, but this is how I did it.

Make a new directory and put in these files, or grab them from here

So let’s start with the Dockerfile :

FROM ubuntu:14.04

MAINTAINER ayoubensalem

RUN apt-get update && apt-get -y install git openssh-server curl software-properties-common
RUN apt-add-repository -y ppa:openjdk-r/ppa \
&& apt-get update \
&& apt-get install -y   openjdk-8-jdk

RUN sed -i 's/PermitRootLogin\ without-password/PermitRootLogin\ no/' /etc/ssh/sshd_config
RUN mkdir -p /var/run/sshd
RUN mkdir /var/lib/jenkins
RUN useradd -m -d /var/lib/jenkins jenkins
RUN cd var/lib/jenkins && mkdir .ssh && chmod 700 .ssh && chown -R jenkins:jenkins .ssh
RUN sudo adduser jenkins sudo
RUN echo "jenkins ALL=NOPASSWD: ALL" >> /etc/sudoers
RUN echo "PasswordAuthentication no">> /etc/ssh/sshd_config

COPY ./run.sh /scripts/run.sh
RUN chmod 777 /scripts/run.sh

WORKDIR var/lib/jenkins

EXPOSE 22

ENTRYPOINT [ "/scripts/run.sh" ]

And the run.sh script :

#!/bin/bash

export BASEDIR="var/lib/jenkins"
export USER_GROUP="jenkins:jenkins"


set_authorized_keys()
{
    echo ${SSH_KEY} >> ${BASEDIR}/.ssh/authorized_keys
    chmod 644 ${BASEDIR}/.ssh/authorized_keys
}

echo ${SSH_KEY}
set_authorized_keys
chown -R ${USER_GROUP} ${BASEDIR}


/usr/sbin/sshd -D

So let’s spin up some containers, and add them as nodes to jenkins master.

We need first to do a quick setup before launching the containers :

Build the image from Dockerfile
First Genereate an SSH KEY for Jenkins user
Export Jenkins PUB KEY as an Environment variable
Run the container and passing the PUB key as an Arguemnt

First let’s build the image :

    $ docker build -t ayoubensalem/jdocker:latest .

then login as jenkins, and :

    $ ssh-keygen -b 2048 -t rsa -f ~/.ssh/id_rsa -q -N ""

    $ export JENKINS_PUB_KEY="$(cat ~/.ssh/id_rsa.pub)"

    $ docker run -d -P -e SSH_KEY=$JENKINS_PUB_KEY ayoubensalem/jdocker:latest

After doing this steps, you should see some running docker containers :

    $ docker ps

Now let’s grab the IPAdress of a running container :

    $ docker inspect <CONTIAINER_ID> | jq -r ".[0].NetworkSettings.Networks.bridge.IPAddress"

Note : You may not have jq installed. ( apt-get install jq )

And let’s try ssh to the container :

    $ ssh jenkins@<CONTAINER_IP>

ET VOILA, we’re able to ssh to the container.

Now the last steps is to configure the new node like so :