using Github releases to build Docker images

docker/Dockerfile_sapsailing_on_sapmachine17

@@ -1,4 +1,8 @@
 FROM sapmachine:17.0.11
+# This Dockerfile assumes that the release to use is provided as
+# ${RELEASE}.tar.gz in the current Docker workspace. Use, e.g.,
+# the configuration/github-download-release-assets.sh script to
+# obtain the tar.gz file for a specific or the latest "main" release.
 ARG RELEASE
 LABEL maintainer=axel.uhl@sap.com
 # Download and extract the release
@@ -9,8 +13,8 @@ COPY vimrc /root/.vimrc
 RUN wget -O /tmp/rds.pem https://s3.amazonaws.com/rds-downloads/rds-combined-ca-bundle.pem \
  && ${JAVA_HOME}/bin/keytool -importcert -alias AWSRDS -file /tmp/rds.pem -keystore ${JAVA_HOME}/lib/security/cacerts -noprompt -storepass changeit \
  && rm /tmp/rds.pem
-RUN wget -O /tmp/${RELEASE}.tar.gz http://releases.sapsailing.com/${RELEASE}/${RELEASE}.tar.gz \
- && tar xzvpf /tmp/${RELEASE}.tar.gz \
+COPY ${RELEASE}.tar.gz /tmp
+RUN tar xzvpf /tmp/${RELEASE}.tar.gz \
  && rm /tmp/${RELEASE}.tar.gz
 COPY env.sh .
 RUN cat env-default-rules.sh >>env.sh