Docker Spring Demo App

This Spring Boot application help you understand how we reduce the size of image of applications while deploying on Docker using jdeps and jlink.

jdeps

• jdeps is responsible for analysing a JAR, with its dependencies, and identifying the parts of the JVM needed to run the application.
• It can out put this to a text file, which can be used by jlink.

Sample Commands

• jdeps applicationname.jar or jdeps -verbose:package applicationname.jar

displays package level dependencies

• jdeps -verbose:class applicationname.jar

displays class level dependencies

• jdeps -profile applicationname.jar

displays the profile containing the package

• jdeps -dotoutput . -verbose applicationname.jar

write class and package level dependencies into file

• jdeps -s applicationname.jar or jdeps -summary applicationname.jar

displays dependencies summary only

jlink

• jlink takes a list of JVM modules, and builds a custom JVM with only those parts present.
• Depending upon our application, this can cut out massive parts of the runtime, reducing our overall Docker image size.

Docker file is created as:

• First download java into the system
• set JAVA_HOME path
• set PATH="$PATH:$JAVA_HOME/bin"
• copy jar into target machine
• run jdeps command to identify the dependencies and write into file
• run jlink command to create custom jre with those modules that are written by jdeps command
• set JAVA_HOME path to the custom jre
• set PATH="$PATH:$JAVA_HOME/bin"
• expose spring boot app into a particular port number and give entry point to run the application.

Build docker image

docker build -f Dockerfile -t applicationname.jar

Run docker image

docker run -p 8085:8085 applicationname.jar