Setup Jenkins - Docker way

While we are adopting the Microservices architecture, it also demands to have an efficient CI/CD tools like jenkins. Along the cloud-native application developement and deployment jenkins can also be run cloud-native.

Since all processes, including software build, test and deployment, are performed every two or four weeks, this is an ideal playground for automation tools like Jenkins: After the developer commits a code change to the repository, Jenkins will detect this change and will trigger the build and test process. So Let's setup Jenkins as a docker container. Step-by-step.

Installing Jenkins the Docker Way

Tools and Versions used

• VM or C2 Instance or a Standalone on-premisis machin

• Docker 1.12.1

• Jenkins 2.32.2

• Job DSL Plugin 1.58

Prerequisites:

• Ubuntu or an Liniux Machine

• Free RAM for the a VM/Machine >~ 4 GB.

• Docker Host is available.

• Tested with 3 vCPU (2 vCPU might work as well).

Step 1: Install a Docker on the Host you provisioned for Jenkins & Connect to the Host via SSH

If you are using a host that already has docker installed, you can skip this step. Make sure that your host has enough memory.

We will run Jenkins in a container to allow for maximum interoperability. This way, we always can use the latest Jenkins version without the need to control the Java version used.

If you are new to Docker, you might want to read .

Installing Docker on Windows and Mac can be a real challenge, but possible: here we will see an efficient way by using a Linux machine.

Prerequisites of this step:

• I recommend having direct access to the Internet: via Firewall, but without HTTP proxy.

• Administration rights on your computer.

Step 2: Download Jenkins Image

This extra download step is optional since the Docker image will be downloaded automatically in step 3 if it is not already found on the system:

The version of the downloaded Jenkins image can be checked with the following command:

We are using version 2.9.13 currently. If you want to make sure that you use the exact same version as I have used in this blog, you can use the imagename jenkins:2.19.3 in all docker commands instead of jenkins only.

Note: The content of the jenkins image can be reviewed on . There, we find that the image has an entrypoint /bin/tini -- /usr/local/bin/jenkins.sh, which we could override with the --entrypoint bash option, if we wanted to start a bash shell in the jenkins image. However, in Step 3, we will keep the entrypoint for now.

Step 3: Start Jenkins in interactive Terminal Mode

In this step, we will run Jenkins interactively (with -it switch instead of -d switch) to better see, what is happening. But first, we check that the port we will use is free:

Since we see that one of the standard ports of Jenkins (8080, 50000) is already occupied and I do not want to confuse the readers of this blog post by mapping the port to another host port, I just stop the cadvisor container for this „hello world“:

Jenkins will be in need of a persistent storage. For that, we create a new folder on the Docker host:

Note: The content of the jenkins image can be reviewed on . There, we find that the image has an entrypoint /bin/tini -- /usr/local/bin/jenkins.sh, which we could override with the --entrypoint bash option, if we wanted to start a bash shell in the jenkins image.

We start the Jenkins container with the jenkins_home Docker host volume mapped to /var/jenkins_home:

Step 4: Open Jenkins in a Browser

Now we want to connect to the Jenkins portal. For that, open a browser and open the URL

In our case, Jenkins is running in a container and we have mapped the container-port 8080 to the local port 8080 of the Docker host. On the Docker host, we can open the URL.

The Jenkins login screen will open:

The admin password can be retrieved from the startup log, we have seen above (0c4a8413a47943ac935a4902e3b8167e), or we can find it by typing

on the mapped jenkins_home folder on the Docker host.

Step 5: Install Plugins

Let us install the suggested plugins:

This may take a while to finish:

Step 6: Create an Admin User and log in

Then we reach a page, where we can create an Admin user:

Let us do so and save and finish.

Note: After this step, I have deleted the Jenkins container and started a new container attached to the same Jenkins Home directory. After that, all configuration and plugins were still available and we can delete containers after usage without loosing relevant information.

I have had a dinner break at this point. Maybe this is the reason I got following message when clicking the „Start using Jenkins“ button?

What ever. After clicking „retry“, we reach the login page:

Create a New Job

In the nex, we will create our first Jenkins job. I plan to trigger the Maven and/or Gradle build of a Java executable file upon detection of a code change.

Step 2: Install the Job DSL Plugin

The can be installed like any other Jenkins plugin:

-> -> ->

-> (with dash between job and dsl; wait for the filter to become active and do not press enter, otherwise you will get an error message)

->

Step 3: Create Job DSL Jenkins Project

We create a Job DSL Job like follows:

->

->

->

Step 4: Configure Job DSL Project

->

-> if you have got a account, fork (originally created by of ) that will allow you to see, what happens with your Jenkins job, if you check in changed code. Moreover the hello world software allows you to perform tests, run Mock services, run JUnit 4 Integration tests and calculate the code coverage using the tool .

->

-> insert:

here, exchange the username oveits by your own username.\

->

Step 5: Prepare Maven Usage

Goto Jenkins -> Manage Jenkins -> Global Tool Configuration (available for Jenkins >2.0)

Scroll down to Maven ->

-> choose Version (3.3.9 in my case)

-> Add a name („Maven 3.3.9“ in my case)

->

Since we have checked „Install automatically“ above, I expect that it will be installed automatically on first usage.

Step 6: Prepare Git Usage

As described in , we need to add the Git username and email address, since Jenkins tries to tag and commit on the Git repo, which requires those configuration items to be set. For that, we perform:

->

->

->

-> scroll down to „Git plugin“

->

Step 7: Create Jenkins Job from Code

Step 7.1 Build Project

->

Step 7.2 (optional): Check Console Output

->

->

->

Step 7.3: Review automatically built Project

->

->

This is showing a build failure, since I had not performed Step 5 and 6 before. In your case, it should be showing a success (in blue). If you are experiencing problems here, check out the Appendices below.

->

-> scroll down to Source Code Management

-> Scroll down to Build Triggers

-> Scroll down to Build

-> verify that „Maven 3.3.9“ is chosen as defined in Step 5

-> enter „-e clean test“ as Maven Goal

->

See, what happens by clicking on:

-> Build History

-> #nnn

->

If everything went fine, we will see many downloads and a „BUILD SUCCESS“:

Appendix A: Solve Git Problem: „tell me who you are“

Symptoms: Git Error: status code 128

In a new installation of Jenkins, Git does not seem to work out of the box. You can see this by choosing the Jenkins project Job-DSL-Hello-World-Job on the dashboard, then click „build now“, if the build was not already automatically triggered. Then:

-> Build History

-> (link works only, if Jenkins is running on localhost:8080 and you have chosen the same job name)

->

There, we will see:

Resolution:

Step 1: Enter Git Username and Email

As described in : we can resolve this issue by either suppressing the git tagging, or (I think this is better) by adding your username and email address to git:

->

->

->

-> scroll down to „Git plugin“

->

Step 2: Re-run „Build Now“ on the Project

To test the new configuration, we go to

-> the and press

->

Now, we should see a BUILD SUCCESS like follows:

-> Build History

-> #nnn

->

If everything went fine, we will a „BUILD SUCCESS“:

Appendix B: Maven Error: Cannot run program „mvn“

Symptoms:

When running a Maven Goal, the following error may appear on the Console log:

Resolution:

Perform Step 5

and

For Test, you can test a manual: choose the correct Maven version, when configuring a Maven build step like in Step 7:

and verify that does not throw the Maven error anymore.

For our case, we need to correct the Job DSL like follows:

In the Script, we had defined the step:

However, we need to define the Maven Installation like follows:

Here, the mavenInstallation needs to specify the exact same name, as the one we have chosen in Step 5 above.

After correction, we will receive the correct Maven goal

-> JobDSL ->

Now, we can check the Maven configuration:

->

->

->

After scrolling down, we will see the correct Maven Version:

DONE

Appendix C: Updating Jenkins

Updating Jenkins (in my case: from 2.32.1 to 2.32.2) was as simple as following the steps below

Note: you might want to make a backup of your jenkins_home though. Just in case…

However, after that, some data was unreadable:

I have clicked

-> Manage Jenkins -> Manage ->

to resolve the issue (hopefully…). At least, after that, the warning was gone.

Appendix D: Job DSL Syntax

The reference for the Job DSL syntax can be found on the . As an example, the syntax of Maven within a Freestyle project can be found on found via the path

> freeStyleJob > steps > maven:

• // Allows direct manipulation of the generated XML.

  (Closure configureBlock)

• // Specifies the goals to execute including other command line options.

  (String goals)

• // Skip injecting build variables as properties into the Maven process.

A Maven example can be found on the same page:

Summary

In this blog post, we have learned how to

1. Start and initialize Jenkins via Docker

2. Prepare the usage of Git and Maven

3. Install the Job DSL Plugin

4. Define a Jenkins Job via Groovy script

We have seen that the usage of the Job DSL is no rocket science. The only topic, we had to take care, is, that Git and Maven need to be prepared for first usage on a Jenkins server.

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