If a Heroku application's DNS is setup correctly then you can usually avoid problems like this on the new Heroku stack (CEDAR). It's important to reread the documentation on using custom domains but also be VERY aware of using naked domains (mysite.com) in your application. This isn't just a Heroku problem, it's a DNS problem. Heroku have recently had a spate of routing issues (usually DDoS attacks) which would have been largely negated by correct DNS setup and either avoiding naked domains or using a DNS host that lets you cname a naked domain to a host.