Java

JRE (Java) Image for Running Apps

The Dockerfile in this directory uses tini application to apply graceful shutdown for its child (java) process. The build section uses JDK's jlink to create a JRE with the core's modules for running applications. In the second section, installing fontconfig and tini packages are necessary.

This image is tested with Oracle JDK 17.

git clone https://github.com/mbizhani/Dockage.git
cd Dockage/Image/Java/
# Copy Oracle 'jdk-xxx_linux-x64.tar.gz' to files directory
docker build -t java:17 .

Now, if you execute docker run --rm -it java:17 ps, the output is:

[INFO  tini (1)] Spawned child process 'ps' with pid '7'
    PID TTY          TIME CMD
      1 pts/0    00:00:00 tini
      7 pts/0    00:00:00 ps
[INFO  tini (1)] Main child exited normally (with status '0')

As you see, due to ENTRYPOINT, the tini is the root process with PID 1. Then tini spawns the next command as its child, so on SIGTERM, the tini process shuts down its child gracefully.

Creating Image for Runnable JAR File

Following Dockerfile is an example to use this base image to run an executable JAR file:

FROM java:17

ENV JAVA_OPTS=""

COPY target/*.jar /app/app.jar

CMD ["sh", "-c", "java ${JAVA_OPTS} -Djava.security.egd=file:/dev/urandom -jar /app/app.jar"]

Note: in the above example, use CMD instead of ENTRYPOINT!

Reference

• Gracefully Shutting Down Applications in Docker