1.. Enable runtime dyno for Heroku with following command :
heroku labs:enable runtime-dyno-metadata -a app-name
2.. Add custom header for all requests. Make the following change in application.rb
config.action_dispatch.default_headers.merge!('X-RELEASE-VERSION' => ENV['HEROKU_RELEASE_VERSION'])
You will receive HEROKU_RELEASE_VERSION values after next deployment.