First look: Jenkins CI with Windows Containers and Docker

In 2014 Microsoft partnered with Docker and the results are in: Windows Containers combined with Docker give the same great experience we've gotten used to in the Linux world.

I've set up a proof of concept to convert the Docker voting app to Windows Containers and have got msbuild.exe working inside a container - now let's move on to the next step - continuous integration with Jenkins CI.

We'll look at creating:

  • a Jenkins master Docker image running on Windows Server Core
  • a Jenkins agent to run headless in a Windows Container

Now the following is a disclaimer - the CloudBees team can tune Jenkins CI far better than I can. Keep an eye out for an official solution on Github from their team of hackers.

Create a Java base image

The main pre-requisite is a JRE and fortunately Stefan Scherer (a fellow Docker Captain) has come up with a base image. We'll take his Java JRE base image as a template:

# escape=`
FROM microsoft/windowsservercore

RUN powershell -Command `  
    wget 'http://javadl.oracle.com/webapps/download/AutoDL?BundleId=210185' -Outfile 'C:\jreinstaller.exe' ; `
    Start-Process -filepath C:\jreinstaller.exe -passthru -wait -argumentlist "/s,INSTALLDIR=c:\Java\jre1.8.0_91" ; `
    del C:\jreinstaller.exe

ENV JAVA_HOME c:\\Java\\jre1.8.0_91  
RUN setx PATH %PATH%;%JAVA_HOME%\bin

CMD [ "java.exe" ]

Build this as a local image:

$ docker build -t windows-java:jre1.8.0_91 .

Before you share or push this image to the public Docker Hub etc bear in mind that Oracle products such as Java have their own EULA and licensing terms.

Create a Jenkins master image

The second pre-requisite for a Jenkins master is to download a Jenkins release as a .war file. Head over to the mirrors site and pick the release you want to work with:

http://mirrors.jenkins-ci.org/war/

Now add a layer to download the .war file:

FROM windows-java:jre1.8.0_91

ENV HOME /jenkins  
ENV JENKINS_VERSION 2.0  
RUN mkdir \jenkins  
RUN powershell -Command "wget -Uri https://updates.jenkins-ci.org/download/war/2.0/jenkins.war -UseBasicParsing -OutFile /jenkins/jenkins.war"

EXPOSE 8080  
EXPOSE 50000

CMD [ "java","-jar", "c:\jenkins\jenkins.war" ]  

If you have issues with the CMD entry please try this instead:

CMD java -jar C:\\jenkins\\jenkins.war  

We have used wget an alias in PowerShell for Invoke-WebRequest. This may be deprecated in the future but is concise enough for our purposes.

  • Port 50000 is used for agent/slave communication
  • Port 8080 provides the web interface

Build the image:

docker build -t jenkins-windows:2.0 .  

You can now run your Jenkins master:

$ docker run --name jenkinsci -p 8080:8080 -p 50000:50000 -d jenkins-windows:2.0

Since the Jenkins 2.0 release security is enabled by default and you will need to find the initial password from the Jenkins container before you can login.

$ docker logs jenkinsci

Connecting to Windows Containers

Once you have found the initial password from the logs, you will need to connect to Jenkins in a web-browser.

Due to networking differences between the Linux and Windows Docker implementation you won't be able to access Jenkins through http://localhost:8080.

  • Type in docker inspect jenkinsci
  • Look for the (NAT) IP address of the container
  • For Windows 10 - use that IP address in place of localhost. For Windows 2016 use the NAT IP address or the IP address of one of your Ethernet adapters such as http://10.95.11.1:8080.

Here's a screenshot of my initial attempt of running the master:

Create a Jenkins agent image

A Jenkins agent image can be created and connected headless later on. This is really useful for running through a CLI or script.

For this image we'll derive from our Java JRE base image, but this time we don't have to fetch a .jar or .war file from the internet. We can fetch it from our running instance of a Jenkins master.

FROM windows-java:jre1.8.0_91

SHELL ["powershell"]  
ARG BASE_URL  
ARG SECRET

RUN (New-Object System.Net.WebClient).DownloadFile('{0}/jnlpJars/slave.jar' -f $env:BASE_URL, 'slave.jar') ;  
ENTRYPOINT ["C:\\Java\\jre1.8.0_91\\bin\\java.exe", "-jar", ".\\slave.jar"]  

For the build pass in the BASE_URL environmental variable like this:

$ docker build --build-arg BASE_URL=http://192.168.0.101:8080 -t jenkins_windows_agent:2.0 .

Now, add a new agent on the Jenkins UI and look for the "secret" needed to authenticate new agents to the master.

Copy the secret and use it when you run your agent:

$ docker run -ti jenkins_windows_agent -jnlpUrl http://192.168.0.101:8080/computer/Windows/slave-agent.jnlp -secret e9714c100fb003e2cef3609b96a255da5f488bc5f195ef6a0fafcebb2836d4e3

You now have a running agent and can run builds and jobs on it:

Wrapping up

You now have a fully-functional Jenkins CI master and agent running on Windows Containers through Docker. Please treat this as a proof of concept and let me know if you have any ideas for improving the level of automation or general experience.

The source for the Dockerfiles is available on Github:

Here are a few areas you could move onto with this basis:

  • Installing custom software such as IIS or .NET into the Jenkins agent
  • Launching agents through the Docker Swarm plugin (classical)
  • Enabling the Blue Ocean UX
  • Integrating containers into the workflow - using a custom Docker registry

See also:

Alex Ellis

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United Kingdom http://alexellis.io/

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