Caching Jar dependencies for Maven
I'm building a Docker image from this Dockerfile:
FROM maven:3.3.3-jdk-8
MAINTAINER Mickael BARON
ADD pom.xml /work/pom.xml
WORKDIR /work
RUN mvn dependency:go-offline --fail-never
ADD ["src", "/work/src"]
RUN ["mvn", "package"]
With this Dockerfile, I force to download the dependencies before packaging my Java project. Thus, I don't have to redownload the dependencies every time I changed a file from my src directory.
But, there is a problem and this problem is depending on the version of Maven (base image). In fact, the dependencies are downloaded but they are not persisted into the ~/.m2 directory of the container. It's empty. Thus, when I change some source file all the dependencies are redownloaded.
However, I noticed that if I change the version of Maven from the base image (for example FROM maven:3.2.5-jdk-8 ), it works.
Very strange, isn't it?
There is a new instruction regarding this topic: https://github.com/carlossg/docker-maven#packaging-a-local-repository-with-the-image
The $MAVEN_CONFIG dir (default to /root/.m2) is configured as a volume so anything copied there in a Dockerfile at build time is lost. For that the dir /usr/share/maven/ref/ is created, and anything in there will be copied on container startup to $MAVEN_CONFIG.
To create a pre-packaged repository, create a pom.xml with the dependencies you need and use this in your Dockerfile. /usr/share/maven/ref/settings-docker.xml is a settings file that changes the local repository to /usr/share/maven/ref/repository, but you can use your own settings file as long as it uses /usr/share/maven/ref/repository as local repo.
I'm afraid it's because of this VOLUME instruction they've added:
https://github.com/carlossg/docker-maven/blame/8ab542b907e69c5269942bcc0915d8dffcc7e9fa/jdk-8/Dockerfile#L11
It makes /root/.m2 a volume and thus any changes to that folder made by build steps are not brought on to the following build containers.
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