Just a friendly heads up to my fellow rails developers. If you are running Pow (http://pow.cx) as a rack application server, you’ll quickly find that localhost on port 80 will never hit docker. This is because the Pow install script enables the PF firewall and adds a rule to forward all port 80 traffic to the Pow server port. Unfortunately, simply stopping the Pow server won’t help as it doesn’t stop PF.
Unless you’re up for reconfiguring Pow to use a different port and thus being stuck appending a port to each launch URL, it appears your only option is to stop PF when you want to use Docker for Mac, and re-enable it when you want to get your Pow on.
Stop PF and use Docker for Mac: sudo pfctl -d
Start PF and use Pow: sudo pfctl -e