We are a company running a website with ~800k unique visitors each month with a constant growth rate of 35-40%. We have just gone from having one server to a dedicated mysql database and an nginx+passenger front end server. We're hitting the next bottleneck after being fine for a little while and are thinking of scaling horizontally by adding a load balanced front-end server solution (We measured the font end to be the bottleneck). The files are obviously located on the single front end server we have now.
What is the best option for keeping the files for the site synced between 2 front end servers? I have googled quite a bit and someone recommended "rsync". The only problem I have with that is the gap you get when the cron job didn't run for a while. Our content updates often and we promote it on the front page. Another solution seems to be NFS and mount up the files to the second front end server as well. Any problems with this solution? Any recommendations are welcome.