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How can I mount a volume to store my .m2 repo so I don't have to download the internet on every build?
My build is a Multi stage build:
FROM maven:3.5-jdk-8 as BUILD
COPY . /usr/src/app
RUN mvn --batch-mode -f /usr/src/app/pom.xml clean package
FROM openjdk:8-jdk
COPY --from=BUILD /usr/src/app/target /opt/target
WORKDIR /opt/target
CMD ["/bin/bash", "-c", "find -type f -name '*.jar' | xargs java -jar"]
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Although there's no functionality in Docker to have volumes at build-time, you can use multi-stage builds, benefit from Docker caching and save time by copying data from other images - be it multi-stage or tagged ones.
Multistage builds let the developer automate the creation process of applications that require some amount of compilation. Developers can create versions that target different OS versions or any other process dependency, which is a big benefit of the approach.
A multistage build allows you to use multiple images to build a final product. In a multistage build, you have a single Dockerfile, but can define multiple images inside it to help build the final image.
Let's say we have two Dockerfiles, one for building the backend and another for building the frontend. We can name them appropriately and invoke the build command two times, each time passing the name of one of the Dockerfiles: $ docker build -f Dockerfile.
You can do that with Docker >18.09 and BuildKit. You need to enable BuildKit:
export DOCKER_BUILDKIT=1
Then you need to enable experimental dockerfile frontend features, by adding as first line do Dockerfile:
# syntax=docker/dockerfile:experimental
Afterwards you can call the RUN command with cache mount. Cache mounts stay persistent during builds:
RUN --mount=type=cache,target=/root/.m2 \
mvn --batch-mode -f /usr/src/app/pom.xml clean package
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