How do I point a docker image to my .m2 directory for running maven in docker on a mac?

Question

When you look at the Dockerfile for a maven build it contains the line:

VOLUME /root/.m2

Now this would be great if this is where my .m2 repository was on my mac - but it isn't - it's in

/Users/myname/.m2

Now I could do:

But then the linux implementation in Docker wouldn't know to look there. I want to map the linux location to the mac location, and have that as part of my vagrant init. Kind of like:

ln /root/.m2 /Users/myname/.m2

My question is: How do I point a docker image to my .m2 directory for running maven in docker on a mac?

Answer 1

How do I point a docker image to my .m2 directory for running maven in docker on a mac?

You rather point a host folder (like /Users/myname/.m2) to a container folder (not an image)

See "Mount a host directory as a data volume":

In addition to creating a volume using the -v flag you can also mount a directory from your Docker daemon’s host into a container.

$ docker run -d -P --name web -v /Users/myname/.m2:/root/.m2 training/webapp python app.py

This command mounts the host directory, /Users/myname/.m2, into the container at /root/.m2.
If the path /root/.m2 already exists inside the container’s image, the /Users/myname/.m2 mount overlays but does not remove the pre-existing content.
Once the mount is removed, the content is accessible again.
This is consistent with the expected behavior of the mount command.

Answer 2

To share the .m2 folder in build step you can overwrite the localRepository value in settings.xml.

Here is the Dockerfile snippet I used to share my local .m2 repository in docker.

FROM maven:3.5-jdk-8 as BUILD

RUN echo \
    "<settings xmlns='http://maven.apache.org/SETTINGS/1.0.0\' \
    xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' \
    xsi:schemaLocation='http://maven.apache.org/SETTINGS/1.0.0 https://maven.apache.org/xsd/settings-1.0.0.xsd'> \
        <localRepository>/root/Users/myname/.m2/repository</localRepository> \
        <interactiveMode>true</interactiveMode> \
        <usePluginRegistry>false</usePluginRegistry> \
        <offline>false</offline> \
    </settings>" \
    > /usr/share/maven/conf/settings.xml;

COPY . /usr/src/app
RUN mvn --batch-mode -f /usr/src/app/pom.xml clean package

FROM openjdk:8-jre
EXPOSE 8080 5005
COPY --from=BUILD /usr/src/app/target /opt/target
WORKDIR /opt/target
ENV _JAVA_OPTIONS '-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005'
ENV swarm.http.port 8080

CMD ["java", "-jar", "app-swarm.jar"]