I was curious whether or not the Sride project was failing. We were about to do a migration once some key integration things were done; doesn't look like they'll finish those.
Or scenarios where you can use EFS to stage data 'for something else' (i.e. shared image / upload content that stages to a CDN, etc.)
Keep in mind (and this comes from hard experience in 'traditional' NFS web server architecture) - if you mount everything on an NFS volume, you ensure that
1) If something goes wrong on that NFS mount, everything goes wrong. (bad code deploy? All nodes are down!)
2) If you rely on an NFS mount to store everything (e.g. trust keystores for JVMs,etc.) your entire infrastructure is dependent on the I/O capabilities of that NFS mount.
3) No matter how clever you are (or how much you trust NFS clients/versions) you will deal with file locking if you are doing a fair amount of read/write from multiple nodes to a single NFS mount.
Short story - EFS will make some of the 'hard' things with distributed nodes possible, but don't make the easy things impossible to troubleshoot.
.... kind of. A reservation is all about planning capacity. If you know (e.g.) that you need two web servers "hot" all the time to serve a base level of traffic, you can pay for that up front either partially or in total (a reservation) at some pretty significant savings. You can add hourly (or spot) capacity as needed - but paying for what you'll be using up front can make AWS very economical.
If you're paying for X1 servers for an extended period of time on an hourly basis, you should be entitled to a thank you note from Jeff Bezos.
To the "free chapter" idea - I think the website has a pretty good prospectus, and compared to other tech books / publishers, it's certainly well worth taking a flyer on it for a maximum of $20.