Update to use new Minideb Ruby base image

https://trello.com/c/dwXqpVAi/968-base-and-builder-images

.ruby-version

@@ -1 +1 @@
-2.7.6
+2.7

Dockerfile

@@ -1,44 +1,32 @@
-ARG base_image=ruby:2.7.6-slim-buster
+ARG base_image=ghcr.io/alphagov/govuk-ruby-base:2.7
+ARG builder_image=ghcr.io/alphagov/govuk-ruby-builder:2.7
 
-FROM $base_image AS builder
+FROM $builder_image AS builder
 
-ENV RAILS_ENV=production GOVUK_APP_NAME=static
-
-RUN apt-get update -qq && \
-    apt-get upgrade -y && \
-    apt-get install -y build-essential nodejs && \
-    apt-get clean
+ENV GOVUK_APP_NAME=static
 
 RUN mkdir /app
 
 WORKDIR /app
 
 COPY Gemfile* .ruby-version /app/
 
-RUN bundle config set deployment 'true' && \
-    bundle config set without 'development test' && \
-    bundle install --jobs 4 --retry=2
+RUN bundle install
 
 COPY . /app
 
-RUN GOVUK_WEBSITE_ROOT=https://www.gov.uk GOVUK_APP_DOMAIN=www.gov.uk bundle exec rails assets:precompile
-
-FROM $base_image
+RUN bundle exec rails assets:precompile && rm -fr /app/log
 
-ENV GOVUK_PROMETHEUS_EXPORTER=true RAILS_ENV=production GOVUK_APP_NAME=static
 
-RUN apt-get update -qy && \
-    apt-get upgrade -y && \
-    apt-get install -y nodejs
+FROM $base_image
 
-RUN groupadd -g 1001 appuser && \
-    useradd appuser -u 1001 -g 1001 --home /app
+ENV GOVUK_APP_NAME=static
 
 COPY --from=builder /usr/local/bundle/ /usr/local/bundle/
 COPY --from=builder /app /app
 RUN mkdir -p /app/public/templates && chown -R 1001:1001 /app/public/templates
 
-USER appuser
+USER app
 WORKDIR /app
 
 CMD bundle exec puma

Gemfile

@@ -1,7 +1,5 @@
 source "https://rubygems.org"
 
-ruby File.read(".ruby-version").chomp
-
 gem "rails", "6.1.6.1"
 
 gem "actionpack-page_caching"

Gemfile.lock

@@ -367,8 +367,5 @@ DEPENDENCIES
   uglifier
   webmock
 
-RUBY VERSION
-   ruby 2.7.6p219
-
 BUNDLED WITH
    2.1.4