Spring Boot Docker 镜像精简，不打包一个大的完整jar文件

A Better Dockerfile

A Spring Boot fat jar naturally has "layers" because of the way that the jar itself is packaged. If we unpack it first it will already be divided into external and internal dependencies. To do this in one step in the docker build, we need to unpack the jar first. For example (sticking with Maven, but the Gradle version is pretty similar):

$ mkdir target/dependency
$ (cd target/dependency; jar -xf ../*.jar)
$ docker build -t myorg/myapp .COPY

with this Dockerfile

Dockerfile

FROM openjdk:8-jdk-alpine
VOLUME /tmp
ARG DEPENDENCY=target/dependency
COPY ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY ${DEPENDENCY}/META-INF /app/META-INF
COPY ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","hello.Application"]COPY

There are now 3 layers, with all the application resources in the later 2 layers. If the application dependencies don’t change, then the first layer (from BOOT-INF/lib) will not change, so the build will be faster, and so will the startup of the container at runtime as long as the base layers are already cached.

We used a hard-coded main application class hello.Application. This will probably be different for your application. You could parameterize it with another ARG if you wanted. You could also copy the Spring Boot fat JarLauncher into the image and use it to run the app - it would work and you wouldn’t need to specify the main class, but it would be a bit slower on startup.