How do YOU get your Java apps running in a cloud?
First you grab a cloud from the sky by, for example, (1) Getting started with a free account on Red Hat OpenShift Online, or (2) locally on your laptop using Red Hat Container Development Kit (CDK) or upstream Minishift on Windows, macOS, and Linux, or (3) using oc cluster up (only on Linux), or (4) by obtaining a login from someone running Red Hat OpenShift on a public or on-premises cloud. Then, you download the oc CLI client tool probably for Windows (and put it on your PATH). Then you select the Copy Login Command from the menu in the upper right corner under your name in the OpenShift Console's UI, and you use, for example, the oc status command.
Great—now you just need to containerize your Java app. You could, of course, start to write your own Dockerfile, pick an appropriate container base image (and discuss Red Hat Enterprise Linux versus CentOS versus Fedora versus Ubuntu versus Debian versus Alpine with your co-workers; and, especially if you're in an enterprise environment, figure out how to have that supported in production), figure out appropriate JVM startup parameters for a container, add monitoring, and so.
But perhaps what you really wanted to do today is...well, just get your Java app running in a cloud!
Read on to find an easier way.
Using Maven
I like to use OpenShift’s Source-to-Image (S2I) builder for this, because I find it to be the fastest and simplest way to go from source code to a running container. Your application’s build probably already produces a self-contained “fat JAR,” because you are likely using a modern framework like Spring Boot, Thorntail.io (formerly known as WildFly Swarm), or Vert.x do. Just to keep it simple for this article, let's use this “Hello World” server with this simplest possible Maven POM. It’s literally as easy as the following command to get it compiled, containerized, and up and running in a minute:
$ oc new-app https://github.com/vorburger/s2i-java-example
If your OpenShift configuration does not have any registered Java builder, or it does not know which one to pick for you (error: multiple images or templates matched "jee"), then you can specify that it should use this one which is provided by the upstream Fabric8 community:
$ oc new-app fabric8/s2i-java~https://github.com/vorburger/s2i-java-example
You can then access the demo simply by exposing the service which new-app created as a route:
$ oc expose svc/s2i-java-example; oc get route s2i-java-example
Gradle, too!
This fabric8/s2i-java S2I builder actually works not just for Maven but also for Gradle build–based projects (I added support for Gradle; see the example project illustrating how to use this), like this:
$ oc new-app fabric8/s2i-java~https://github.com/fabric8io-images/s2i --context-dir=java/examples/gradle --name s2i-gradle-example
By the way, if your build produces a JAR file in another location or with another name than what the S2I Java image expects to find it, you can place a .s2i/environment file into your project to override ARTIFACT_COPY_ARGS or JAVA_APP_JAR or set any custom fixed environment variables your application may require.
And Java 11!
The fabric8/s2i-java S2I image now has functionality for building with and running under Java 11:
$ oc new-app fabric8/s2i-java:latest-java11~https://github.com/vorburger/s2i-java-example
The Java 11 feature is brand new and is likely to evolve; community feedback would be welcomed regarding any required JVM startup parameter adjustments, work related to a smaller JDK base image using Java 11 modularity with jlink for perhaps faster startup and somewhat reduced JRE memory consumption (and which, hopefully, will be less huge), using a more minimal container base image, or maybe a 32-bit variant. Contributions are most welcome!
Note: the images provided by the Fabric8 community are not supported by Red Hat.
Last updated: January 12, 2024