Ruby has a serious scalability problem most Rubyists are unaware of. When you lookup the IP address for a hostname, the entire Ruby process blocks by default. If you have a slow DNS server, your process can grind to a halt waiting for hostname resolution. Ruby comes standard with a fix, resolv-replace, which provides a DNS resolver that does not block the entire process. It does however block the Thread, like any other instance of blocking I/O.

So I wrote an EventMachine-aware DNS resolver that ensures that your asynchronous operations don't block while performing DNS resolution. Take a look at em-resolv-replace and give it a whirl.

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