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Setup and manage a Jenkins continuous integration cluster in EC2

Project description

The CGCloud Jenkins project contains the roles for running a distributed continuous integration environment in EC2 with one Jenkins master VM and multiple slave VMs. A Jenkins slave is a machine that the master delegates builds to. Slaves are launched on demand and are shutdown after a certain amount of idle time. The different slave roles are blueprints for setting up a slave VM that has the necessary prerequisites for running a particular Jenkins build.


Activate the virtualenv cgcloud was installed in and install cgcloud-jenkins:


   virtualenv cgcloud
   source cgcloud/bin/activate
   pip install cgcloud-jenkins
   export CGCLOUD_PLUGINS="cgcloud.jenkins:$CGCLOUD_PLUGINS"

If you get DistributionNotFound: No distributions matching the version for cgcloud-jenkins, try running pip install --pre cgcloud-jenkins.

Running cgcloud list-roles should now list the additional roles defined in the plugin:


Master And Slave Roles

The plugin defines a role for the master (jenkins-master) and various slave roles for running builds for certain building CGL projects. There are also a bunch of generic slaves that are not customized for a particular project.

The master (jenkins-master) is a long-running box that hosts the Jenkins web application. The Jenkins installation (code and data) is cordoned off in the home directory of a separate jenkins user. That home directory actually resides on a secondary EBS volume whose life cycle is independent from that of the master box, i.e. VM instance. This allows us to update the OS of the master without having to setup Jenkins from scratch every time we do so.

The remaining roles define the Jenkins slaves. A Jenkins slave is a short-running box with which the master establishes an SSH connection for the purpose of triggering a remote build. The CGCLoud Jenkins plugin (this project) is used to create the VM images and register them with the master such that the master can launch a slave instance when needed to run a remote build on the platform provided by the slave.


Jenkins is a continuous integration server/web applicaton running on the jenkins-master. Jenkins uses so called projects that define where to get the source, how to build and test the source and which build artifacts to archive. Builds can be run automatically whenever a push is made, on a fixed schedule or manually. Builds are executed by an agent. Agents can run locally on the Jenkins master or remotely on one or more slaves. Jenkins uses its own plugin system to extend and modify the default behavior. We use the EC2 plugin which allows us to create slaves on demand in EC2 from images created by cgcloud in conjunction with this project. Mind the distinction between CGCloud Jenkins which is plugs into CGCLoud and the hundreds of plugins that extend Jenkins.

The Jenkins web UI can always be accessed by tunneling port 8080 through SSH. Running cgcloud ssh jenkins-master sets up the necessary port forwarding. Authorization and authentication in Jenkins itself is disabled on a fresh instance but can be enabled and further customized using Jenkins plugins. Note: Anyone with SSH access to the master can access Jenkins and do anything with it.

Tutorial: Creating a Continuous Integration Environment

In this tutorial we’ll create a continuous integration environment consisting of a Jenkins master and several slaves. The tutorial assumes that you completed the Quickstart section of the CGCloud README.

Creating The Master

Create the Jenkins master instance:

cgcloud create jenkins-master

As a test, SSH into the master as the administrative user:

cgcloud ssh -a jenkins-master

The administrative user has sudo privileges. Its name varies from platform to platform but cgcloud keeps track of that for you. For yet another test, SSH into the master as the jenkins user:

cgcloud ssh jenkins-master

This is the user that the Jenkins server runs as.

Next, create an image of the master such that you can always recreate a 100% identical clone:

cgcloud stop jenkins-master
cgcloud image jenkins-master
cgcloud terminate jenkins-master
cgcloud recreate jenkins-master

The first command is necessary to stop the master because only a stopped instance can be imaged. The image command creates the actual AMI image. The terminate command disposes of the instance. This will delete the / partition while leaving the /var/lib/jenkins partition around. The latter is stored on a separate EBS volume called jenkins-data. In other words, the terminate command leaves us with two things: 1) the AMI for a master box and 2) the Jenkins data volume. The recreate command then creates a new instance from the most recently created image and attaches the jenkins-data volume that instance.

Creating The Slaves

Open a new shell window and create the first slave:

cgcloud list-roles
cgcloud create docker-jenkins-slave

SSH into it:

cgcloud ssh -a docker-jenkins-slave

Notice that

  • The admin user has sudo rights:

    sudo whoami
  • The builds directory in the Jenkins user’s home is symbolically linked to ephemeral storage:

    sudo ls -l ~jenkins
  • git and docker are installed:

    git --version
    docker --version

Now stop, image and terminate the box:

cgcloud stop docker-jenkins-slave
cgcloud image docker-jenkins-slave
cgcloud terminate docker-jenkins-slave

Finally, register all slaves with the master:

cgcloud register-slaves jenkins-master docker-jenkins-slave

The register-slaves command adds a section to Jenkins’ config.xml defines how to spawn an EC2 instance of docker-jenkins-slave from the AMI we just created. The slave description also associates the slave with the label docker. If a project definition requests to be run on slaves labelled docker, an instance will be created from the AMI. Once the instance is up, the Jenkins master will launch the agent on via SSH. Finally, the master will ask the agent to run a build for that project. If a slave labelled docker already exists, it will be used instead of creating a new one. You can customize how may concurrent builds run on each slave by increasing the number of agents running on a slave. By default only one slave per role will be launched but you can configure Jenkins to launch more than one if the queue contains multiple builds for a given label.

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