Ash HN:For Dockerized apps why is it a bad practice to use NFS for shared data?

Because old versions of AWS didn't support NFS. This is called Elastic Stockholm Syndrome (ES2).

Not really a bad practice per se. It's just that if your app requires high performance, then NFS can become a bottlebeck. It's not any fault of NFS, but NFS was not designed to run at high speed. But in the absence of anything else or if your app is like any other regular app, NFS is perfect to use, especially NFS 4.