Restart Gitaly when Ruby version changes

We saw in production that Gitaly didn't restart when we upgraded from
Ruby v2.6.6 to v2.7.2. We now signal a HUP to restart Gitaly gracefully
when the version changes.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/273108

changelogs/unreleased/sh-restart-gitaly-on-ruby-version-change.yml

+---
+title: Restart Gitaly when Ruby version changes
+merge_request: 4696
+author:
+type: fixed

files/gitlab-cookbooks/gitaly/recipes/enable.rb

@@ -116,6 +116,13 @@ version_file 'Create version file for Gitaly' do
   notifies :hup, "runit_service[gitaly]"
 end
+# If a version of ruby changes restart gitaly-ruby
+version_file 'Create Ruby version file for Gitaly' do
+  version_file_path File.join(working_dir, 'RUBY_VERSION')
+  version_check_cmd '/opt/gitlab/embedded/bin/ruby --version'
+  notifies :hup, "runit_service[gitaly]"
+end
+
 consul_service 'gitaly' do
   action Prometheus.service_discovery_action
   socket_address node['gitaly']['prometheus_listen_addr']

spec/chef/recipes/gitaly_spec.rb

@@ -77,6 +77,15 @@ RSpec.describe 'gitaly' do
       expect(chef_run.version_file('Create version file for Gitaly')).to notify('runit_service[gitaly]').to(:hup)
     end
+    it 'creates a default RUBY_VERSION file and restarts service' do
+      expect(chef_run).to create_version_file('Create Ruby version file for Gitaly').with(
+        version_file_path: '/var/opt/gitlab/gitaly/RUBY_VERSION',
+        version_check_cmd: '/opt/gitlab/embedded/bin/ruby --version'
+      )
+
+      expect(chef_run.version_file('Create Ruby version file for Gitaly')).to notify('runit_service[gitaly]').to(:hup)
+    end
+
     it 'populates gitaly config.toml with defaults' do
       expect(chef_run).to render_file(config_path).with_content { |content|
         expect(content).to include("socket_path = '/var/opt/gitlab/gitaly/gitaly.socket'")