Misc fixes to the Wolfi-based Dockerfile (#114)

In `Dockerfile.wolfi`:

* switch back to the `java` user for running the application itself
* use newer `ENV=` syntax
* remove `/app/.git` from the image to decrease size

Dockerfile.wolfi

@@ -1,7 +1,5 @@
 FROM docker.elastic.co/wolfi/jdk:openjdk-21.35-r1-dev@sha256:d7ca36452a68f28e4c4683062241e817b548844820a0ffd087451214e61eb188
 
-# TODO we may need to use root for some steps in the Dockerfile, but we should switch to
-# another user for running the application itself inside the container
 USER root
 
 # ------------------------------------------------------------------------------
@@ -14,15 +12,15 @@ RUN apk update && apk add --no-cache curl make
 # jruby install steps below have been adapted from:
 # https://github.com/jruby/docker-jruby/blob/f325c86e2c2ca0bbe82f64c0aded0719372507fa/9.4/jdk21/Dockerfile
 
-ENV JRUBY_VERSION 9.4.8.0
-ENV JRUBY_SHA256 347b6692bd9c91c480a45af25ce88d77be8b6e4ac4a77bc94870f2c5b54bc929
+ENV JRUBY_VERSION=9.4.8.0
+ENV JRUBY_SHA256=347b6692bd9c91c480a45af25ce88d77be8b6e4ac4a77bc94870f2c5b54bc929
 RUN mkdir /opt/jruby \
   && curl -fSL https://repo1.maven.org/maven2/org/jruby/jruby-dist/${JRUBY_VERSION}/jruby-dist-${JRUBY_VERSION}-bin.tar.gz -o /tmp/jruby.tar.gz \
   && echo "$JRUBY_SHA256 /tmp/jruby.tar.gz" | sha256sum -c - \
   && tar -zx --strip-components=1 -f /tmp/jruby.tar.gz -C /opt/jruby \
   && rm /tmp/jruby.tar.gz
 RUN mkdir -p /usr/local/bin && ln -s /opt/jruby/bin/jruby /usr/local/bin/ruby
-ENV PATH /opt/jruby/bin:$PATH
+ENV PATH=/opt/jruby/bin:$PATH
 
 # skip installing gem documentation
 RUN mkdir -p /opt/jruby/etc \
@@ -34,18 +32,23 @@ RUN mkdir -p /opt/jruby/etc \
 RUN gem install bundler rake net-telnet xmlrpc
 
 # don't create ".bundle" in all our apps
-ENV GEM_HOME /usr/local/bundle
+ENV GEM_HOME=/usr/local/bundle
 ENV BUNDLE_SILENCE_ROOT_WARNING=1 \
-       BUNDLE_APP_CONFIG="$GEM_HOME"
-ENV PATH $GEM_HOME/bin:$PATH
+    BUNDLE_APP_CONFIG="$GEM_HOME"
+ENV PATH=$GEM_HOME/bin:$PATH
 
 # adjust permissions of a few directories for running "gem install" as an arbitrary user
 RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
 
 # ------------------------------------------------------------------------------
 # install the application
 
+# TODO we should look at finding a better way to get the application artifact into
+# the container image, since we are adding lots of stuff here that we do not need
+# and may not want (do we need vendor/ after the make install below, for instance?),
+# contributing to increased image size; for now at least we can remove `.git` (below)
 COPY . /app
+
 WORKDIR /app
 
 # skip jenv/rbenv setup
@@ -54,8 +57,13 @@ ENV IS_DOCKER=1
 RUN make clean install
 
 # ------------------------------------------------------------------------------
-# remove now-unnecessary packages, as well as the package manager itself
+# remove now-unnecessary packages and directories
+
+RUN apk del curl make git \
+    && apk --purge del apk-tools \
+    && rm -rf /app/.git
 
-RUN apk del curl make && apk --purge del apk-tools
+# switch back to the base image's default user when running the application
+USER java
 
 ENTRYPOINT [ "/bin/bash" ]