Switch back to -slim image for final stage to decrease image size

This requires us to duplicate environment variables.

The commit also disables --reproducible mode for kaniko – our images are
not reproducible in the first place (because we run apt-update) and
using the option leads to weird dates being shown for the images.

Closes #58

.gitlab-ci.yml

@@ -24,7 +24,6 @@ docker-image:
       --context "${CI_PROJECT_DIR}"
       --dockerfile "${CI_PROJECT_DIR}/Dockerfile"
       --destination "${DOCKER_IMAGE_NAME}"
-      --reproducible
   rules:
     - if: $CI_COMMIT_BRANCH
       exists:

Dockerfile

@@ -3,7 +3,10 @@
 # Make sure RUBY_VERSION matches the Ruby version in .ruby-version and Gemfile
 # renovate: datasource=docker depName=registry.docker.com/library/ruby
 ARG RUBY_VERSION=3.4.2
-FROM registry.docker.com/library/ruby:$RUBY_VERSION AS base
+
+# ###################################################################
+# Throw-away build stage to reduce size of final image
+FROM registry.docker.com/library/ruby:$RUBY_VERSION AS build
 
 # Rails app lives here
 WORKDIR /rails
@@ -14,10 +17,6 @@ ENV RAILS_ENV="production" \
   BUNDLE_PATH="/usr/local/bundle" \
   BUNDLE_WITHOUT="development"
 
-
-# Throw-away build stage to reduce size of final image
-FROM base AS build
-
 # Install packages needed to build gems
 RUN apt-get update -qq && \
   apt-get install --no-install-recommends -y build-essential git libvips pkg-config
@@ -38,8 +37,18 @@ RUN bundle exec bootsnap precompile app/ lib/
 RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile
 
 
+# ###################################################################
 # Final stage for app image
-FROM base
+FROM registry.docker.com/library/ruby:$RUBY_VERSION-slim
+
+# Rails app lives here
+WORKDIR /rails
+
+# Set production environment
+ENV RAILS_ENV="production" \
+  BUNDLE_DEPLOYMENT="1" \
+  BUNDLE_PATH="/usr/local/bundle" \
+  BUNDLE_WITHOUT="development"
 
 # Install packages needed for deployment
 RUN apt-get update -qq && \