Kubernetes: Building and deploying a Java service with Jenkins

Kubernetes has become the de facto container orchestration platform to run applications on. Java applications are no exception to this. When using a PaaS provider to give you a hosted Kubernetes, sometimes that provider also provides a CI/CD solution. However this is not always the case. When hosting Kubernetes yourself, you also need to implement a CI/CD solution.

Jenkins is a popular tool to use when implementing CI/CD solutions. Jenkins can also run quite easily in a Kubernetes environment. When you have Jenkins installed, you need to have a Git repository to deploy your code from, a Jenkins pipeline definition, tools to wrap your Java application in a container, a container registry to deploy your container to and some files to describe how the container should be deployed and run on Kubernetes. In this blog post I'll describe a simple end-to-end solution to deploy a Java service to Kubernetes. This is a minimal example so there is much room for improvement. It is meant to get you started quickly.

Running Reactive Spring Boot on GraalVM in Docker

GraalVM is an open source polyglot VM which makes it easy to mix and match different languages such as Java, Javascript and R. It has the ability (with some restrictions) to compile code to native executables. This of course offers great performance benefits. Recently, GraalVM Docker files and images have become available. See here.

Since Spring Boot is a popular Java framework and reactive (non blocking) RESTful services/clients implemented in Spring Boot are also interesting to look at, I thought; lets combine those and produce a Docker image running a reactive Spring Boot application on GraalVM.

I've used and combined the following

• Building a Reactive RESTful Web Service
• Spring Boot with Docker and Running Spring Boot in a Docker container on OpenJDK, Oracle JDK, Zulu on Alpine Linux, Oracle Linux, Ubuntu
• Oracle's GraalVM Docker images
• (my very own) Ubuntu Development VM (requires VirtualBox, Vagrant)

As a base I've used the code provided in the following Git repository here. In the 'complete' folder (the end result of the tutorial) is a sample Reactive RESTful Web Service and client.

Automate the installation of Oracle JDK 8 and 10 on RHEL and Debian derivatives

Automating the Oracle JDK installation on RHEL derivatives (such as CentOS, Oracle Linux) and Debian derivatives (such as Mint, Ubuntu) differs. This is due to different package managers and repositories. In this blog I'll provide quick instructions on how to automate the installation of Oracle JDK 8 and 10 on different Linux distributions. I chose JDK 8 and 10 since they are currently the only Oracle JDK versions which receive public updates (see here).

Running Spring Boot in a Docker container on OpenJDK, Oracle JDK, Zulu on Alpine Linux, Oracle Linux, Ubuntu

Spring Boot is great for running inside a Docker container. Spring Boot applications 'just run'. A Spring Boot application has an embedded servlet engine making it independent of application servers. There is a Spring Boot Maven plugin available to easily create a JAR file which contains all required dependencies. This JAR file can be run with a single command-line like 'java -jar SpringBootApp.jar'. For running it in a Docker container, you only require a base OS and a JDK. In this blog post I'll give examples on how to get started with different OSs and different JDKs in Docker. I'll finish with an example on how to build a Docker image with a Spring Boot application in it.