Info

example code from document on layered buildpacks

Usage

• download a dummy project from initializr

VERSION=2.3.4.RELEASE
curl https://start.spring.io/starter.zip -d bootVersion=$VERSION -d dependencies=web -o /tmp/demo.zip
unzip /tmp/demo.zip
rm -fr mvnw mvnw.cmd HELP.md

• containerize using maven

mvn spring-boot:build-image

docker image ls | grep buildimage

buildimage                         0.1.0-SNAPSHOT          357fb481ea71   41 years ago    225MB

• run

docker run -d -p 8080:8080  buildimage:0.1.0-SNAPSHOT

• test

curl -v -X POST http://localhost:8080/test

< HTTP/1.1 200 
< Content-Length: 0
< HTTP/1.1 200 
< Content-Length: 0

TODO: add configuration to the pom.xml to avoid pulling the ubuntu as a base image.

Without Maven

the standard scenario

export IMAGE=basic-layered
mvn clean package
docker build -f Dockerfile -t $IMAGE .

will avoid downloading the image adoptopenjdk:11-jre-hotspot as builder

docker run -p 8080:8080 -d $IMAGE

• check log for errors

docker logs $(docker container ls  -a | grep $IMAGE | awk '{print $1}')

Troubleshoot Errors

when copying of the exploded java directories fails for some reason, the error is

Error: Could not find or load main class org.springframework.boot.loader.JarLauncher

and

[ERROR] Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:2.3.4.RELEASE:repackage (repackage) on project buildimage: Execution repackage of goal org.springframework.boot:spring-boot-maven-plugin:2.3.4.RELEASE:repackage failed: Unable to find main class -> [Help 1]

to investigate build the builder image permanently

docker build -f Dockerfile.builder -t buider .

and connect to it

Timings

---|--- clear run | 5+ min fully timed clear run, including image downloads | 15+ min rerun with no changes | 50.255 s rebuild modified | 01:17 min

Manual Build in Steps

build with Dockerfile.builder / Dockerifile.runner

docker build -t builder -f Dockerfile.builder

docker build -t runner -f Dockerfile.runner .

docker run -d -p 8080:8080 runner

Cleanup

docker image rm $(docker image ls | grep buildimage | awk '{print $3}')
docker image rm $(docker image ls | grep paketobuildpacks | awk '{print $3}')
docker stop $(docker container ls | grep $IMAGE | awk '{print $1}' )
docker container rm  $(docker container ls -a | grep $IMAGE | awk '{print $1}' )
docker image rm $IMAGE

docker image prune -f

docker container rm -f $(docker container ls -a | grep runner | awk '{print $1}' )
docker image rm builder runner

See Also

• collection of containerized spring app build optimization options
• official Spring Boot Docker documentation, see in partcular the Spring Boot Layer Index section