Create a Dockerfile to build and run the app

.dockerignore

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+/log/
+/node_modules/
+/tmp/

Dockerfile

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+FROM ruby:2.6.2-alpine AS web
+
+RUN apk add build-base
+RUN apk add tzdata
+RUN apk add postgresql-dev
+RUN apk add yarn
+
+# Set up install environment
+ENV APP_HOME /app
+
+RUN mkdir -p ${APP_HOME}
+WORKDIR ${APP_HOME}
+
+ARG RAILS_ENV
+ENV RAILS_ENV ${RAILS_ENV:-production}
+ENV NODE_ENV ${RAILS_ENV:-production}
+
+RUN echo "Building with RAILS_ENV=${RAILS_ENV}"
+# End
+
+# Install Ruby dependencies
+COPY Gemfile ${APP_HOME}/Gemfile
+COPY Gemfile.lock ${APP_HOME}/Gemfile.lock
+
+RUN gem install bundler
+RUN bundle install --frozen --retry 3 --without development test
+# End
+
+# Install JavaScript dependencies
+COPY package.json ${APP_HOME}/package.json
+COPY yarn.lock ${APP_HOME}/yarn.lock
+
+RUN yarn install --frozen-lockfile --production
+# End
+
+# Copy app code (sorted by vague frequency of change for caching)
+RUN mkdir -p ${APP_HOME}/log
+RUN mkdir -p ${APP_HOME}/tmp
+
+COPY config.ru ${APP_HOME}/config.ru
+COPY Rakefile ${APP_HOME}/Rakefile
+
+COPY public ${APP_HOME}/public
+COPY vendor ${APP_HOME}/vendor
+COPY bin ${APP_HOME}/bin
+COPY lib ${APP_HOME}/lib
+COPY config ${APP_HOME}/config
+COPY db ${APP_HOME}/db
+COPY app ${APP_HOME}/app
+# End
+
+RUN RAILS_ENV=production DFE_SIGN_IN_ISSUER= DFE_SIGN_IN_REDIRECT_URL= DFE_SIGN_IN_IDENTIFIER= DFE_SIGN_IN_SECRET= bundle exec rake assets:precompile
+
+EXPOSE 3000
+
+CMD [ "rails", "server" ]