Improve Docker image sizes by using multistage build

[OSMOSA44]

Hi,

When you write

ADD $APIMAN_DISTRO /tmp/apiman-distro-vertx.zip

RUN bsdtar xvf /tmp/apiman-distro-vertx.zip --strip-components=1 -C /opt/apiman && \
    rm /tmp/apiman-distro-vertx.zip && \
    chmod +x /opt/apiman/apiman-gateway.sh

The rm /tmp/apiman-distro-vertx.zip is inefficient because ADD and RUN command generate two distinct image layers and a layer cannot modify another layer

To delete the zip file, you have to download, unzip and delete on the same layer

For example (with use of wget)

RUN wget -O /tmp/apiman-distro-vertx.zip $APIMAN_DISTRO && \
    bsdtar xvf /tmp/apiman-distro-vertx.zip --strip-components=1 -C /opt/apiman && \
    rm /tmp/apiman-distro-vertx.zip && \
    chmod +x /opt/apiman/apiman-gateway.sh

You can use this usefull tool dive to inspect the image efficiency

Regards

[msavy]

Thanks for your comment, @OSMOSA44!

This is something I did deliberately and have decided to keep.

The separate ADD step allows me to substitute the default remote file with a file copied from the Docker build directory (i.e. local file to build system). This is very useful when doing development, testing, and performing manual releases, working with snapshots, etc.

Unfortunately, this technique does not work with the curl approach, as curl can't transparently access the local filesystem in the same way the ADD command can (which has special capabilities).

e.g:

docker build --build-arg APIMAN_DISTRO=apiman-distro-wildfly-3.1.0-SNAPSHOT-overlay.zip .

Potentially, I could use a container compaction technique like docker build --squash or DockerSlim.

[OSMOSA44]

You can use multi stage Docker build

See this Dockerfile

Testing commands below

docker buildx build --platform=linux/amd64 --build-arg APIMAN_DISTRO=apiman-distro-vertx-3.0.0.Final.zip -t apiman/vertx-gateway:3.0.0.Final.local .

or

docker buildx build --platform=linux/amd64 --build-arg APIMAN_VERSION=3.0.0.Final -t apiman/vertx-gateway:3.0.0.Final.remote .

Nota: To avoid warning and potentially errors, I have added the platform target parameter as i work on MacBook Pro M1

[msavy]

Thanks, that's a good idea. I'll chat with the team and we'll do some experiments.