multi-module Maven project on Dockers

Question

I have a multi-module maven project where the single modules are all runnable microservice applications containing their own Dockerfile, so in production every module will be a containerized application.

The parent project, which contains the child-modules only contains the parent pom.xml and the docker-compose.yml

I have tried to use the following Dockerfile (on sub-module level):

FROM sgrio/java-oracle

RUN apt-get update

RUN apt-get install -y maven

COPY ../pom.xml /usr/local/service/Oogaday/pom.xml

COPY pom.xml /usr/local/service/Oogaday/OogadayApi/pom.xml

COPY src /usr/local/service/Oogaday/OogadayApi/src

WORKDIR /usr/local/service/Oogaday/OogadayApi/

RUN mvn package -DskipTests

CMD ["java","-jar","org.oogaday.api-1.0-SNAPSHOT-jar-with-dependencies.jar"]

But I am getting a security error because I am trying to copy the parent pom.xml file (which is not placed in the directory from which I am running the build).

So is there a way to build a maven based sub-module with parent pom?

Answer 1

This is my suggestion, you should take advantage the more you can of docker cache.

Assume this multi-module project pom layout:

+-- my-project
   +-- module1
   |   `-- pom.xml
   +-- module2
   |   `-- pom.xml
    `- pom.xml

Dockerfile:

# cache as most as possible in this multistage dockerfile.
FROM maven:3.6-alpine as DEPS

WORKDIR /opt/app
COPY module1/pom.xml module1/pom.xml
COPY module2/pom.xml module2/pom.xml

# you get the idea:
# COPY moduleN/pom.xml moduleN/pom.xml

COPY pom.xml .
RUN mvn -B -e -C org.apache.maven.plugins:maven-dependency-plugin:3.1.2:go-offline

# if you have modules that depends each other, you may use -DexcludeArtifactIds as follows
# RUN mvn -B -e -C org.apache.maven.plugins:maven-dependency-plugin:3.1.2:go-offline -DexcludeArtifactIds=module1

# Copy the dependencies from the DEPS stage with the advantage
# of using docker layer caches. If something goes wrong from this
# line on, all dependencies from DEPS were already downloaded and
# stored in docker's layers.
FROM maven:3.6-alpine as BUILDER
WORKDIR /opt/app
COPY --from=deps /root/.m2 /root/.m2
COPY --from=deps /opt/app/ /opt/app
COPY module1/src /opt/app/module1/src
COPY module2/src /opt/app/module2/src

# use -o (--offline) if you didn't need to exclude artifacts.
# if you have excluded artifacts, then remove -o flag
RUN mvn -B -e -o clean install -DskipTests=true

# At this point, BUILDER stage should have your .jar or whatever in some path
FROM openjdk:8-alpine
WORKDIR /opt/app
COPY --from=builder /opt/app/<path-to-target>/my-1.0.0.jar .
EXPOSE 8080
CMD [ "java", "-jar", "/opt/app/my-1.0.0.jar" ]