[igul222]

I think Heroku's default Rails app server is WEBRick: https://devcenter.heroku.com/articles/ruby#webserver

[hayksaakian]

im pretty sure it's thin

[matthewrudy]

It will run thin if the gem is installed. Otherwise it falls back to Webrick. Rack itself favours thin, puma, and webrick (in that order). https://github.com/rack/rack/blob/6829a8a0f416ea49a18f1e3e53...