I have not googled coding stuff in a few weeeks so Stack Overflow and its snotty gatekeeping is dead. That "Please post full line" is answered now. And thankfully lots of people like YOU will soon be out of a job.
I do performance WP hosting and would like to try out EFS but it is not available locally yet.
What I do is use redundant RDS, ELB etc but on all the WP installs have an inhouse plugin that with any change it ioniced rsyncs that vhosts tree to all webservers and ssh's a command to them all to dump their WP cache.
It may seem hackish but the sites absolutely fly, have tried several clustered file systems but all that complexity hits reliability and speed.