> Unfortunately, I get the exact same connection error message > from Heroku when using an IP that dig has no problem connecting to > (e.g. Google's public DNS server 8.8.8.8):
I just dug some more -- Turns out the Errno::ECONNREFUSED has nothing to do with the nameserver you're querying. For some reason, dnsruby is trying to connect back to localhost when the error is raised (on line 87 of select_thread.rb): https://github.com/pupeno/dnsruby/blob/master/lib/Dnsruby/select_thread.rb#L75-91 Indeed, it seems appropriate that the EC2 server hosting your dyno should refuse that connection! So, I think this means dnsruby is a no-go on Heroku.
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