502 bad gateway:<p>1) Check that your Mongrel is still running. If not, restart it.<p>1b) #1 could be done automatically by e.g. "god" monitoring software or monit.<p>2) Add a configuration setting in Nginx which will give people a better error message if this happens again. <i>error_page 502 503 504 /50x.html;</i> You can customize 50x.html as much as you wish.<p>3) See my upcoming blog post about preventing downtime as a solo entrepreneur.