Speedup docker build time (#463)

Dockerfile

@@ -7,6 +7,10 @@ FROM registry.docker.com/library/ruby:$RUBY_VERSION-slim as base
 # Rails app lives here
 WORKDIR /rails
 
+# Install base packages
+RUN apt-get update -qq && \
+    apt-get install --no-install-recommends -y curl libvips postgresql-client
+
 # Set production environment
 ENV RAILS_ENV="production" \
     BUNDLE_DEPLOYMENT="1" \
@@ -18,8 +22,7 @@ ENV RAILS_ENV="production" \
 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 libpq-dev libvips pkg-config
+RUN apt-get install --no-install-recommends -y build-essential git libpq-dev pkg-config
 
 # Install application gems
 COPY Gemfile Gemfile.lock ./
@@ -40,10 +43,8 @@ RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile
 # Final stage for app image
 FROM base
 
-# Install packages needed for deployment
-RUN apt-get update -qq && \
-    apt-get install --no-install-recommends -y curl libvips postgresql-client && \
-    rm -rf /var/lib/apt/lists /var/cache/apt/archives
+# Clean up installation packages to reduce image size
+RUN rm -rf /var/lib/apt/lists /var/cache/apt/archives
 
 # Copy built artifacts: gems, application
 COPY --from=build "${BUNDLE_PATH}" "${BUNDLE_PATH}"