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Spring Boot Dockerize

official docker guide from spring.io. official docker getting started from spring.io.

  1. dockerfile + fatjar
  2. easy setup
  3. dockerfile + exploded jar
  4. leverages layer system of docker
  5. dockerfile multistage build (build + execution in container)
  6. allows build to run everywhere where docker is installed
  7. google jib (maven + gradle plugins)
  8. no docker installation needed on machine where the build runs
  9. no dockerfile needed
  10. opinionated about usage of docker layers

dockerfile + fatjar

FROM openjdk:14-jdk-slim
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} myApp.jar
ENTRYPOINT ["java","-jar","/myApp.jar"]

dockerfile + exploded jar

  • To explode a jar: jar -xf myapp.jar
  • to execute a exploded jar you can start
  • JarLauncher: java org.springframework.boot.loader.JarLauncher
  • Your main class: java -cp BOOT-INF/classes:BOOT-INF/lib/* de.example.MyApplication

Dokerfile to use exploded jar: 

FROM openjdk:8-jre-alpine
ARG DEPENDENCY=target/dependency
COPY --from=builder ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY --from=builder ${DEPENDENCY}/META-INF /app/META-INF
COPY --from=builder ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","de.example.MyApplication"]

dockerfile multistage build (build + execution in container)

build jar in multistage build:

FROM openjdk:8-jdk-alpine as build
WORKDIR /workspace/app
COPY mvnw .
COPY .mvn .mvn
COPY pom.xml .
COPY src src

RUN ./mvnw install -DskipTests

FROM openjdk:8-jdk-alpine
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} myApp.jar
ENTRYPOINT ["java","-jar","/myApp.jar"]

explode jar in multistage build:

FROM openjdk:8-jdk-alpine AS builder
WORKDIR target/dependency
ARG APPJAR=target/*.jar
COPY ${APPJAR} app.jar
RUN jar -xf ./app.jar

FROM openjdk:8-jre-alpine
VOLUME /tmp
ARG DEPENDENCY=target/dependency
COPY --from=builder ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY --from=builder ${DEPENDENCY}/META-INF /app/META-INF
COPY --from=builder ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","com.example.MyApplication"]

the maven wrapper seems to ignore http proxies which are set with the http_proxy or the https_proxy environmental variable.Instead you can set a proxy for maven with MAVEN_OPTS environmental variables: export MAVEN_OPTS=-Dhttp.proxyHost=bla - DhttpProxyPort=80 -Dhttps.proxyHost=bla - DhttpsProxyPort=80

google jib (maven + gradle plugins)

google jib maven plugin gradle plugin

You do not need to install docker on the client to create a docker image with jib.

devtools

Developer tools are automatically disabled when running a fully packaged application. Launch via java -jar or special classloader is considered a production environment so they are deactivated. source.

This will have effects on several property defaults like spring.h2.console.enabled. For full list see.