Java 11 Support Preview is available in Jenkins 2.155+

This is a joint blogpost prepared by the Java 11 Support Team.
On Dec 18 (4PM UTC) we will be also presenting the Java 11 Preview Support at the Jenkins Online Meetup
(link)

Jenkins Java

Jenkins, one of the leading open-source automation servers, still supports only Java 8.
On September 25 OpenJDK 11 was released.
This is a Long-Term-Support which will stay around for years,
and in the Jenkins project we are interested to offer a full support of this version.
Over the last year many contributors have been working towards enabling support for Java 11 in the project (Jenkins JEP-211).
It was a thorny path,
but now, on behalf of the Jenkins Platform SIG,
we are happy to announce preview availability of Java 11 support in Jenkins weekly releases!

Why do we need preview availability for Java 11?
It offers Jenkins contributors and early adopters a way
to try out the changes before the general availability release happens early next year.
It should help us to get more exploratory testing and, hopefully,
resolve most of the issues before Java 11 is officially supported in Jenkins.

In this blog post we will describe how to run with Java 11,
and how to investigate compatibility issues and report them.

Background

As you probably remember,
in June 2018 we had an online hackathon targeting Java 10+ support in Jenkins.
As a part of the hackathon,
we provided the experimental support of Java 11.
This event was a big success for us,
and we were able to get Jenkins running with Java 10 and 11-ea,
including major features like Jenkins Pipeline, JobDSL, Docker/Kubernetes plugins, Configuration as Code, BlueOcean, etc.
It gave us confidence that we can provide Java 11 support in Jenkins without major breaking changes.
After the hackathon, Oleg Nenashev created
JEP-211: Java 10+ support in Jenkins (was later adjusted to target Java 11 only).
Platform Special Interest Group
has been also founded to coordinate the Java 11 support work
and other platform support efforts (packaging, operating system support, etc.).

A group of contributors continued working on Java 11 support,
mostly focusing on upstreaming functional patches,
enabling Java 11 support in development tools,
testing and addressing known compatibility issues.
See the Platform SIG meeting notes for detailed status updates.
Starting from Jenkins 2.148, Jenkins successfully runs with latest OpenJDK 11 releases on various Linux and Windows platforms.
We performed a LOT of automated and exploratory tests, Jenkins plugins appear to work well with some exceptions (see below).
There is ongoing test automation effort towards the GA releases,
but we were able to successfully run Jenkins core tests,
full Acceptance Test Harness,
and Plugin Compat Tester for recommended plugins.
We also deployed a temporary
Experimental Update Center for Java 11
which allows quickly delivering fixes for Java 11 early adopters.
Jenkins 2.155+ defaults to this update center when running with Java 11,
and that’s why we announce preview availability for this version.

On Nov 19, 2018 we presented the current Java 11 support status at the Platform SIG meeting
slides,
and we agreed that we would like to proceed with the preview availability so that
we can offer something for evaluation to Jenkins users.
By the next meeting on Dec 04, all blockers have been addressed,
and the Platform SIG meeting signed off the Java 11 preview availability.

Running Jenkins and Java 11 in Docker

Starting from Jenkins 2.155, we provide Docker images for the Jenkins master and agent.
All these images are based on the official
openjdk:11-jdk image maintained by the Docker Community.
There were discussions about migrating to other base images,
but we decided to exclude it from the Preview Availability scope.
Similarly, we do not provide Alpine images for now.

Jenkins master image

Java 11 support is now provided as a part of the official
jenkins/jenkins image.
You can run the Jenkins with Java 11 simply as:

docker run -p 8080:8080 -p 50000:50000 jenkins/jenkins:jdk11

The following tags are available:

  • jdk11 – Latest weekly release with Java 11 support
  • 2.155-jdk11 – Weekly releases packaged with Java 11

The image is fully compatible with
jenkins/jenkins documentation,
e.g. you can use plugins.txt to install plugins, mount volumes and pass extra options via environment variables.

Agent images

If you use containerized agents via Docker or Kubernetes plugins,
we have also released official Docker images for Jenkins agents:

All images use the latest-jdk11 image tag for JDK11 bundles.
And sorry for the obsolete names!

Experimental Jenkins master images

In order to simplify testing, we also provide some experimental images on DockerHub.
We set up a continuous delivery flow for them,
so you can get patches without waiting for Jenkins weekly releases.

  • jenkins4eval/blueocean-platform-support
    Equivalent of jenkinsci/blueocean

    • Tag: latest-jdk11
    • The image bundles all Jenkins Pipeline and Blue Ocean patches required to run on Java 11
    • If you want to try Pipeline, use this image
  • jenkins/jenkins-experimental
    Equivalent of jenkins/jenkins

    • Tag: latest-jdk11
    • The image is released from the java11-support feature branch in the Jenkins core
    • The branch may be slightly ahead or behind the master branch,
      we may use the branch to quickly deliver patches to Java 11 users

Eventually we will move the experimental flow to the new jenkins4eval organization
being created as a part of JEP-217.

Running jenkins.war with Java 11

Running without Docker is not that trivial,
because Jenkins depends on some modules which have been removed from Java 11.
We plan to address it in the General Availability release somehow (see JENKINS-52186),
but for now some manual actions are required to run Jenkins WAR with Java 11.

  1. Download Jenkins WAR for 2.155
  2. Download the following libraries to the same directory as jenkins.war
  3. Run the following command:
Run Jenkins with ${JAVA11_HOME}/bin/java 
    -p jaxb-api.jar:javax.activation.jar --add-modules java.xml.bind,java.activation 
    -cp jaxb-core.jar:jaxb-impl.jar 
    -jar jenkins.war --enable-future-java --httpPort=8080 --prefix=/jenkins

Known compatibility issues

To help users to track down the compatibility issues,
we have created a new Known Java 11 Compatibility Issues Wiki page.

Several important issues and obstacles:

  • Pipeline: Support Plugin has a known issue
    with context persistency when running with Java 11 (JENKINS-51998)

    • We have deployed a temporary fix to the
      Experimental Update Center for Java 11.
      Fix version: 3.0-java11-alpha-1
    • If you use Jenkins Pipeline, make sure you run with this fix.
      Otherwise the jobs will fail almost immediately
    • When updating instances to Java 11, make sure there is no running Pipelines
  • JENKINS-54305
    JDK Tool Plugin does not offer installers for JDK 11
  • JENKINS-52282
    Java Web Start is no longer available in Java 11, so it is no longer possible to start agents from Web UI.
    We do not plan to provide a replacement.

We also know about some minor incompatibilities in other plugins,
but we do not consider them as blockers for preview availability.

Reporting compatibility issues

If you discover any Java 11 incompatibilities, please
report issues in our bugtracker.
Please set java11-compatibility labels for such issues
so that they automatically appear on the Wiki page and get triaged.

For the security issues please use the standard
vulnerability reporting process.
Although we will be fixing Java 11 specific issues in public while it is in the preview,
following the security process will help us to investigate impact on Java 8 users.

Java 11 Support Team

Once Java 11 support is released, we expect reports of regressions in plugins and Jenkins core.
One of the concerns are exotic platforms with native libraries, and of course other Java versions.
There is also a risk of 3rd-party library incompatibilities with Java 11.
To mitigate the risks, we have created a
Java 11 Support Team.
This team will be focusing on triaging the incoming issues,
helping to review pull requests and, in some cases, delivering the fixes.
The process for this team is documented in JEP-211.

We do not expect the Java 11 Support Team to be able to fix all discovered issues,
and we will be working with Jenkins core and plugin maintainers to get the fixes delivered.
If you are interested to join the team,
reach out to us in the Platform SIG Gitter Channel.

Contributing

We will appreciate any kind of contributions in the Java 11 effort,
including trying out Jenkins with Java 11, reporting and fixing compatibility issues.

  • If you want to do the exploratory testing,
    we recommend to try out Java 11 support at one of your test instances.
    Such testing will be much appreciated,
    especially if you use some service integration plugins or exotic platforms.
    The issue reporting guidelines are provided above
  • If you are a plugin developer/maintainer,
    we would appreciate if you could test your plugin with Java 11.
    In order to help with that, we have created a Wiki page with
    Java 11 Developer guidelines.
    This page explains how to build and test plugins with Java 11,
    and it also lists known issues in development tools

Whatever you do, please let us know about your experience by sending a message to
the Platform SIG mailing list.
Such information will help us a lot to track changes and contributions.
Any other feedback about the migration complexity will be appreciated!

What’s next?

On Dec 18 (4PM UTC) we will be presenting the Java 11 Preview Support at the Jenkins Online Meetup
(link).
At this meetup we will summarize the current Java 11 Preview support status.
If you are a plugin developer, we will also organize separate sessions about testing plugins with Java 11 and about common best practices for fixing compatibility issues.
Please follow the Platform SIG announcements if you are interested.

In the next weeks we will focus on addressing feedback from early adopters and
fixing the discovered compatibility issues.
We will also continue working on Java 11 support patches towards the general availability next year (JENKINS-51805).
In addition to that, we will start working on Java 11 support in subprojects,
including Jenkins X and Jenkins Evergreen.

Originally posted on Jenkins Blog
Author: oleg_nenashev

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