Artifact caching for Multi-stage Builds about docker-maven

[carlossg]

Now that .m2 is no longer a volume this should work

FROM maven:alpine
WORKDIR /usr/src/app
COPY pom.xml .
RUN mvn -B -e -C -T 1C org.apache.maven.plugins:maven-dependency-plugin:3.0.2:go-offline
COPY . .
RUN mvn -B -e -o -T 1C verify

FROM openjdk:alpine
COPY --from=0 /usr/src/app/target/*.jar ./

[mukhtar]

Facing similar issue. This proposal if/when done will help address the issue.

[awhitford]

Sadly, I don't see how that RUN --mount proposal will truly solve the problem. A Dockerfile may be built on a Windows machine, a Mac, or a Linux machine. The mount destination for MVN_REPO is a decision for the runner/builder, not the Dockerfile.

One idea that I can imagine is to declare a volume mount requirement. Imagine something like: REQUIRED_VOLUME MVN_REPO is declared that essentially says, Volume MVN_REPO needs to be defined. Then, that logical volume may be used in the Docker build (or run). If the volume is not defined, it could error out. I could see this feature useful for all sorts of reasons, like declaring a destination for log files or database content.

[sixcorners]

Try using this

FROM maven
WORKDIR /usr/src/app
# /root/.m2 is a volume :(
ENV MAVEN_OPTS=-Dmaven.repo.local=../m2repo/
COPY pom.xml .
# v2.8 doesn't work :(
RUN mvn -B -e -C -T 1C org.apache.maven.plugins:maven-dependency-plugin:3.0.2:go-offline
COPY . .
RUN mvn -B -e -o -T 1C verify

FROM openjdk
COPY --from=0 /usr/src/app/target/*.jar ./

It caches the local repo like how the python onbuild Dockerfile does it. MAVEN_OPTS is needed because someone made /root/.m2/ a volume so stuff that goes in there doesn't get saved. verify is needed because "dependency:go-offline" doesn't work. You could probably just omit the "dependency:go-offline" part.
This sets it up so that changes to the pom.xml result in cache invalidation and redownload but other changes can just use the cache.

Edit: using a newer dependency:go-offline because the older one doesn't work.

[Algram]

@sixcorners I am trying to do exactly the same thing you are doing, but for some reason my maven offline install fails and says it can't find the POM.xml for some maven internal projects. Have you had a similar problem?