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?

Wennerholn

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.

Titillate

By some reasons this not working for me. In build stage maven still download dependencies... Any suggestions? – Upcast

Yes, I would like to know more: what host OS, image OS, maven version are you using? Could you detail those information in a new question? – Titillate

It is just docker cant share volumes while build. Just in run, github.com/docker/docker/issues/14080 – Upcast

Very confusing why you're mounting a Maven folder and running a Python script :) In any case, wouldn't this cause permissions issues when maven (eventually) downloads and writes files within the volume as its uid/gid?) – Motorcade

@Motorcade like any mounted folder, you must make sure your image uses the right uid/gid if it intent to persist data in said mounted folder indeed. – Titillate

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"]

Invent

You must still be mounting a volume here to make /root/Users/myname/ work within the container? You also don't need a "target" folder for a JAR to be ran – Motorcade

Answer 3

Here are the Dockerfiles and docker-compose for example project containing one spring service and any other services;

Spring-service dockerfile

FROM maven:3.5-jdk-8-alpine 

WORKDIR /app

COPY . src

CMD cd src ; mvn spring-boot:run

docker-compose.yml

version: '3'

services:

  account-service:
    build:
      context: ./
      dockerfile: Dockerfile
    ports:
      - "8080:8080"
    volumes:
      - "${HOME}/.m2:/root/.m2"

Here in docker-compose we make volumes for our local .m2 repo and container one.

Hallah

You should consider not using mvn to run the app. The JDK isn't needed, and this causes larger image sizes – Motorcade

Answer 4

I am using maven:3-amazoncorretto-17 as my base image.

Using some info from Arun A's answer I was able to come up with a pretty simple solution. The tricky part (for me) was figuring out where the settings.xml needed to go inside the container. Also, this example is mounting just settings.xml.

Using docker-compose:

    volumes:
      - "~/.m2/settings.xml:/usr/share/maven/conf/settings.xml"

Or docker run -v

$ docker run -v ~/.m2/settings.xml:/usr/share/maven/conf/settings.xml maven:3-amazoncorretto-17 

This syntax should work on both Windows and Mac.

Skidway