Configure JRebel with Docker containers – Tech Tip #81

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JRebel allows you to skip build and redeploy process by instantly deploying your application to the application server of your choice. It is supported in all the major IDEs such as NetBeans, Eclipse, and IntelliJ. It is also supported in a wide variety of application servers such as JBoss EAP, WildFly, WebLogic, WebsFear (err, WebSphere), Tomcat, and many others.

You can easily get started with JRebel in JBoss Developer Studio  or Integrate JRebel with JBoss on your local desktop. It can also be easily used with JBoss Developer Studio and Ticket Monster on OpenShift.

This Tech Tip will explain how do you set up JRebel with Docker containers. Specifically, we’ll use the sample application provided by Java EE 7 Hands-on Lab (jrebel branch), JBoss Tools with Eclipse Mars M5, and running the sample application in WildFly Docker container.

Many thanks to Adam Koblentz (@akoblentz) for helping me through the steps!

Lets get started!

Install JRebel in Eclipse

JRebel runs in three modes:

  • Local: App server is running from inside the IDE
  • External: App server is running from outside the IDE, such as using CLI, but on the same machine
  • Remote: App server is running on a different machine, VM, container, or cloud

Docker containers need to be configured using the “remote” mode.

  1. Install JBoss Tools  as explained at tools.jboss.org/downloads/. JRebel’s remote mode can only be enabled using the IDE. Install JRebel plugin from Eclipse Marketplace.

Package rebel.xml and rebel-remote.xml with the WAR

These files define the location of classes and resources in your archive.

  1. Clone the Java EE 7 HOL repo:
  2. Import the Maven project (from the solution directory) in the IDE, right-click on the project, select JRebel menu, and click on “Enable JRebel Nature”. This will generate rebel.xml in src/main/resources directory and would look something like:
  3. Right-click on the project again, and select “Enable Remoting”. This generates rebel-remote.xml, in src/main/resources directory again, and will look like:
    This needs to be done on the machine where JRebel will be used in the IDE. This will ensure that the public key is generated appropriately.
  4. Package your application as
    This will package rebel.xml and rebel-remote.xml in the WAR file.

Configure and Run the Application Server

Application server needs to know about JRebel agent and platform-specific library. Both of these files are available from Eclipse if JRebel was installed earlier. On Mac these files are available in eclipse/mars/m5/eclipse/plugins/org.zeroturnaround.eclipse.embedder_6.1.1.RELEASE-201503121801/jr6/jrebel/ directory. The exact name would very likely differ in your case.

  1. Build the image using the Dockerfile:
    The key parts in this image are:

    1. Using the official jboss/wildfly Docker image
    2. Copying the JRebel agent and platform-specific library to the image
    3. Configuring application server such that it knows about the “remote” mode and platform-specific library
    4. Start WildFly
    5. Downloads the pre-built WAR file from GitHub. This will not work for you, and you’ll need to replace it with something like:
      This WAR file is the same that was generated earlier.
  2. Actually build the image as:
  3. Run the container as:
    and this should show something like:
    JRebel license information is a good sign that everything is configured properly.

    If you used Docker Machine to Setup Docker Host then the application should now be accessible at 192.168.99.100:8080/movieplex7/.

Configure Eclipse

Last step is to configure Eclipse so that it knows where the application is deployed.

  1. In Eclipse, right-click on the project, select JRebel, Advanced Properties
  2. Click on “Edit” on next to “Deployment URLs”
  3. Click on Add and specify the URL of the application, 192.168.99.100:8080/movieplex7/ in our case.
  4. Click on Continue, Apply, OK.

Voila, the configuration is now complete.

Now changing any class, adding any method, updating any entity or HTML or JSF page will push the changes to the Docker container instantly. No need to redeploy the application.

Enjoy!

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4 thoughts on “Configure JRebel with Docker containers – Tech Tip #81”

  1. Hey Arun,
    This is a good idea, in addition it will be good to run your server in debug mode and expose the debugger port trough the container by running: docker run -it -p 8080:8080 -p 8787:8787 javaee7-hol ( supposing 8787 is the debuging port)

    Then attach your IDE to the debugger, in netbeans it can be done by going to Debug Menu then Attach debugger, and enter the IP / port you’ve configured earlier.

  4. This configures Wildfly as a service. Journald then captures all data printed to stdout, but then logs are not well structured. I tought about something like apache/mod_journald. Just additional/optional logger(logger handler?) that would write to journald using it’s API, adding additional tags that would allow to simply browse/filter logs (e.g. by level). Systemd is now much a standard in Linux distros (in particular RedHat 😉 ) Here is a good article about journald http://0pointer.de/blog/projects/journal-submit.html

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