Dockerfile Overwrite ARG values

Question

I have a Dockerfile that has Scala and SBT as below:

# Scala and sbt Dockerfile
# Scala and SBT forked from: https://github.com/hseeberger/scala-sbt
# Adds Docker client installation additionally

# Pull base image
FROM  openjdk:$JAVA_VERSION

ARG SCALA_VERSION
ARG SBT_VERSION

# Scala expects this file
RUN touch /usr/lib/jvm/java-$JAVA_VERSION-openjdk-amd64/release

# Install Scala
## Piping curl directly in tar
RUN \
  curl -fsL http://downloads.typesafe.com/scala/$SCALA_VERSION/scala-$SCALA_VERSION.tgz | tar xfz - -C /root/ && \
  echo >> /root/.bashrc && \
  echo 'export PATH=~/scala-$SCALA_VERSION/bin:$PATH' >> /root/.bashrc

# Install sbt
RUN \
  curl -L -o sbt-$SBT_VERSION.deb http://dl.bintray.com/sbt/debian/sbt-$SBT_VERSION.deb && \
  dpkg -i sbt-$SBT_VERSION.deb && \
  rm sbt-$SBT_VERSION.deb && \
  apt-get update && \
  apt-get install sbt && \
  sbt sbtVersion

Now if I want to use this as my base image, I have the following question:

1. Can I overwrite the ARG parameters in my new Dockerfile which will use the one above as a base image?

Answer 1

Each Dockerfile produces an immutable image. So you need first build an specific base image, and then build your own FROM it.

You can take this approach:

Dockerfile.base:

# Scala and sbt Dockerfile
# Scala and SBT forked from: https://github.com/hseeberger/scala-sbt
# Adds Docker client installation additionally

# Pull base image
ARG JAVA_VERSION
FROM  openjdk:$JAVA_VERSION

ARG SCALA_VERSION
ARG SBT_VERSION

# Scala expects this file
RUN touch /usr/lib/jvm/java-$JAVA_VERSION-openjdk-amd64/release

# Install Scala
## Piping curl directly in tar
RUN \
  curl -fsL http://downloads.typesafe.com/scala/$SCALA_VERSION/scala-$SCALA_VERSION.tgz | tar xfz - -C /root/ && \
  echo >> /root/.bashrc && \
  echo 'export PATH=~/scala-$SCALA_VERSION/bin:$PATH' >> /root/.bashrc

# Install sbt
RUN \
  curl -L -o sbt-$SBT_VERSION.deb http://dl.bintray.com/sbt/debian/sbt-$SBT_VERSION.deb && \
  dpkg -i sbt-$SBT_VERSION.deb && \
  rm sbt-$SBT_VERSION.deb && \
  apt-get update && \
  apt-get install sbt && \
  sbt sbtVersion

Your child Dockerfile Dockerfile.mine:

ARG JAVA_VERSION
ARG SCALA_VERSION
ARG SBT_VERSION
FROM basejava:java-$JAVA_VERSION-scala-$SCALA_VERSION-sbt-$SBT_VERSION
# Your app stuf here
# ...
# ...

Build example:

 export JAVA_VERSION=latest
 export SCALA_VERSION=1.8
 export SBT_VERSION=0.13.9
 docker build . \
   -f Dockerfile.base \
   --build-arg JAVA_VERSION=$JAVA_VERSION \
   --build-arg SCALA_VERSION=$SCALA_VERSION \
   --build-arg SBT_VERSION=$SBT_VERSION \
   -t basejava:java-$JAVA_VERSION-scala-$SCALA_VERSION-sbt-$SBT_VERSION

 docker build . \
   -f Dockerfile.mine \
   --build-arg JAVA_VERSION=latest \
   --build-arg SCALA_VERSION=1.8 \
   --build-arg SBT_VERSION=0.13.9
   -t myjava:java-$JAVA_VERSION-scala-$SCALA_VERSION-sbt-$SBT_VERSION

---

Approach 2, ONBUILD, mentioned by zigarn.

Dockerfile.base:

# Scala and sbt Dockerfile
# Scala and SBT forked from: https://github.com/hseeberger/scala-sbt
# Adds Docker client installation additionally

# Pull base image
ONBUILD ARG JAVA_VERSION
FROM  openjdk:$JAVA_VERSION

ONBUILD ARG SCALA_VERSION
ONBUILD ARG SBT_VERSION

# Scala expects this file
ONBUILD RUN touch /usr/lib/jvm/java-$JAVA_VERSION-openjdk-amd64/release

# Install Scala
## Piping curl directly in tar
ONBUILD RUN \
  curl -fsL http://downloads.typesafe.com/scala/$SCALA_VERSION/scala-$SCALA_VERSION.tgz | tar xfz - -C /root/ && \
  echo >> /root/.bashrc && \
  echo 'export PATH=~/scala-$SCALA_VERSION/bin:$PATH' >> /root/.bashrc

# Install sbt
ONBUILD RUN \
  curl -L -o sbt-$SBT_VERSION.deb http://dl.bintray.com/sbt/debian/sbt-$SBT_VERSION.deb && \
  dpkg -i sbt-$SBT_VERSION.deb && \
  rm sbt-$SBT_VERSION.deb && \
  apt-get update && \
  apt-get install sbt && \
  sbt sbtVersion

Your child Dockerfile.mine

FROM basejava
# Base ONLBUILD instructions are automatically inserted here.
# Your app stuf here
# ...
# ...

Build:

docker build . -f Dockerfile.base -t basejava

export JAVA_VERSION=latest
export SCALA_VERSION=1.8
export SBT_VERSION=0.13.9
docker build . \
   -f Dockerfile.mine \
   --build-arg JAVA_VERSION=$JAVA_VERSION \
   --build-arg SCALA_VERSION=$SCALA_VERSION \
   --build-arg SBT_VERSION=$SBT_VERSION \
   -t myjava:java-$JAVA_VERSION-scala-$SCALA_VERSION-sbt-$SBT_VERSION

Answer 2

ARG values are defined at build time.
Once your base image is built, you cannot just change the --build-arg to get another SCALA_VERSION inside your final image (or you have to install it again in you new Dockerfile)

The present Dockerfile is like a template for other Dockerfile.
You could use the ONBUILD instruction to effectively do the installations during the build of other images using this one as base image.