Jenkins-Lab

This project describes some functionalities included in Jenkins, how to set them up and their use. These functionalities are listed below:

• Execute Scripts on remote host using SSH.
• Jenkins DSL (Domain Specific Language).
• Jenkinsfile.
• Creation of slave nodes using Docker containers.

Getting started

These instructions will get you through the steps to run locally your Jenkins instance using Docker containers.

Prerequisites

• Docker CE.
• Docher compose.

Installing

Run Jenkins master

To persist Jenkins configuration, the first thing to do is to create and change the ownership of the directory jenkins-home which will be located in the folder jenkins-server of this repo. Docker image from Jenkins runs under the user jenkins (UID 1000). Start the Docker services described in the docker-compose.yml file by running the script start-services.sh.

./start-services.sh

This script creates and changes the user of the directory jenkins-home and initiates Compose file located in the root of this repo, creating two containers: Jenkins master and a remote host. First one will expose two ports:

• 8080 to access UI.
• 53801 to access Jenkins via the Jenkins CLI.

You will see these two services by running the command docker-compose ps. Access Jenkins UI on http://localhost:8080. At this point, you will be prompted to unlock Jenkins by inserting the admin password which you can get directly from the jenkins_server container:

docker container exec jenkins_server cat /var/jenkins_home/secrets/initialAdminPassword

You might face a No such File or Directory error: Wait for Jenkins service to be up and running (IT could take some seconds).

Insert the outcome of the above command in the UI. For your convenience, change it for an easy-to-remember password.

Jenkins DSL

Jenkins jobs can be created programmatically using Jenkins DSL. 3 simple jobs for this lab can be found at this link.

Run Jenkins DSL

Required Plugins or Others

• Job DSL plugin (This plugin is installed when spinning up docker-compose. See plugins.txt).

Set Up

Follow the steps listed in the setup section of the repo described above.

Run scripts in a remote host using SSH

Required Plugins or Others

• SSH plugin (This plugin is installed when spinning up docker-compose. See plugins.txt).

Set Up

After downloading the required plugin, go to Manage Jenkins -> Configure System. In the section SSH remote hosts, add a new SSH site with the following information:

• Hostname: remote_host (This corresponds to the service name of the remote host in the docker-compose file).
• Port: 22
• Credentials: Create a SSH Username with Private Key type credential. Use as Private key the one you will find in the .ssh folder of the Jenkins master here and user remote_user.

Use the remote-connection-dsl job created through Jenkins DSL to run a simple command in the remote host (To be fixed: If the build result keeps giving you UNSTABLE, go to configure ans click on save button. It should fix this problem).

Jenkins CLI

Required Plugins or Others

• jenkins-cli.jar (go to Manage Jenkins -> Jenkins CLI and click on the file name to download it).

Set Up

1. Put the jar file in the root of this repo.
2. Configure the SSH server port: Go to Manage Jenkins -> Configure Global Security -> SSH Server. Fix it to the port 53801 (This port is exposed in the docker-compose file).
3. SInce this is a user-based SSH connection, you need to publish the public SSH key of the machine you are intended to connect from in the config of the admin user: Go to configure of the admin user and paste the SSH public key in the field SSH Public Keys.
4. Run the script jenkins-cli.sh.

This example script describes how to use Jenkins CLI running the following scenarios:

1. List the current jobs. This list will be saved in a file named job.txt.

2. Extract their config.xml file. They will be created in the root of this repo.

3. Run the seed job (Jenkins DSL).

Use of Docker nodes to run Jenkins Jobs

Required Plugins or Others

• Docker plugin (This plugin is installed when spinning up docker-compose. See plugins.txt).
• Docker host (a Debian VM in VirtualBox is used for this lab). This host will need to have installed Docker CE.

Set Up

Docker plugin

Go to Manage Jenkins -> Manage nodes and clouds. Go to Configure Clouds and add a new Docker cloud. In here, fill it in with the following information:

• Docker Host URI: tcp://<Docker_host_IP_address>:4243.

After that, add a new Docker Agent Template. This template will create a new container based in the image you add in the Docker Image field which will build your app. This image should include at least the following configuration (You can take a look at this Dockerfile example):

• sshd service running on port 22.
• Jenkins user with password (This will be necessary in the field Connect method -> Connect with SSH of the cloud configuration).
• Required application dependencies for the build.

The following is a simple Docker Agent configuration:

• labels: docker-slave

• Docker image: crileroro/jenkins-slave:ubuntu-18.04

• Connect Method: Connect with SSH

  • SSH Key: Use Configured SSH Credentials

• Pull strategy: Pull once and update latest.

VM set up

In case you may want to create a Debian VM, run the script configure-debian-slave.sh to set up a simple Docker host. This script will run the following configuration:

• Install Docker CE.
• Install Docker Compose.
• Enable Docker remote API: The Docker daemon can listen for Docker Engine API requests via 3 different types of socket: unix, tcp and fd. By default, unix socket is enabled (/var/run/docker.sock). Due to the fact that unix socket works for exchanging data between processes executing on the same host OS, this does not help if you want to access the Docker Rest API remotely. This is why it is necessary to enable TCP socket (/lib/systemd/system/docker.service).

If you are creating your Docker host using a VM in VirtualBox/VMware, attach it to a Bridged Adapter. This option will allow you to have more interaction between your host and guest machine (your VM will have its own IP address, in the same network range of your host machine). It becomes handy as Jenkins will spin up a new container on a random port and you VM should be able to be contactable on that specific port. (The use of the networking mode NAT is cumbersome as you should port forward a range of ports to your VM.)

After you have set up both your Docker host (VM) and the Docker Plugin, create a job and the General section, flag the option Restrict where this project can be run to select the label of your Docker Agent.

Jenkinsfiles