Add support for EU region (+ follower database)

[ezekg]

Use Cloudflare's geo-based load balancing to route between our US and EU apps (it can route to a hostname, i.e. a different Heroku app). Also will need to use octopus to add support for a follower database in the EU region (writes will still be done in the US - hopefully that's performant).

See:

• https://devcenter.heroku.com/articles/heroku-postgres-follower-databases#create-a-follower
• https://github.com/thiagopradi/octopus/wiki/Replication-with-Rails-on-Heroku
• https://medium.com/kkempin/postgresql-master-slave-replication-on-heroku-with-ruby-on-rails-bf0eb8d69fe
• https://web.archive.org/web/20131021050541/http://ctshryock.com/posts/2013/10/16/distributing-reads-to-a-follower-on-heroku.html

[ezekg]

Related to #156.

[ezekg]

Relevant: https://github.com/thiagopradi/octopus/issues/317 (might be an outdated Octopus issue).

[ezekg]

Apparently you can fork Heroku apps still, just with a CLI add-on. Forking creates new databases (one for each "color" ENV var), but keeps the master set to the original database, which is what we want.

heroku fork --from keygen-sh --to keygen-sh-eu --region eu

See: https://devcenter.heroku.com/articles/app-migration#forking

We should do that for both APIs.

[ezekg]

See: https://devcenter.heroku.com/articles/managing-add-ons#using-the-command-line-interface-attaching-an-add-on-to-another-app