Jeff Geerling shares his tips for “Getting the best performance out of Amazon EFS”. Given how (still) new the Amazon EFS is and how limited is the documentation of the best practices, this stuff is golden.
tl;dr: EFS is NFS. Networked file systems have inherent tradeoffs over local filesystem access—EFS doesn’t change that. Don’t expect the moon, benchmark and monitor it, and you’ll do fine.