(One of the product managers on the Amazon EFS team here). Drupal is a common application that customers use with EFS, both in combination with a CDN and without. The following are two important considerations when running Drupal on an NFS service like EFS:
i) You should configure the OPcache so that it does not revalidate its cache on every request. Cache validation uses stat() in a serial loop on potentially hundreds of files, where each stat() would add O(ms) to the request.
ii) We recommend you store log files locally. NFS does not define an atomic O_APPEND operation, so appends require a file lock to prevent interleaving with appends from other clients. I've seen PHP application do 100s of file locks to a log file per request, each adding O(ms) to the total request latency. This is what you'd like to avoid.
i) You should configure the OPcache so that it does not revalidate its cache on every request. Cache validation uses stat() in a serial loop on potentially hundreds of files, where each stat() would add O(ms) to the request.
ii) We recommend you store log files locally. NFS does not define an atomic O_APPEND operation, so appends require a file lock to prevent interleaving with appends from other clients. I've seen PHP application do 100s of file locks to a log file per request, each adding O(ms) to the total request latency. This is what you'd like to avoid.