I noticed you can create EBS volumes for each Layer in your Opsworks stack.
My question: is the EBS volume shared amongst the Instances of a Layer, or does each Instance gets its own EBS? (so, is one EBS created, or are many?)
Why: I'm creating a custom database layer, and have configured my database to write its data on the EBS. Of course I don't want separate database instances in the database layer stomping on each others data. So I would prefer separate EBS volumes, but haven't seen anything canonical about behavior either way.
While it's not cool to answer my own question, I've confirmed results experimentally, and am noting my results for people From The Future. We whom are from the past salute you!
EBS volumes are not shared across the instances of a layer - in fact, each instance gets its own EBS. When you start and stop an instance it mounts the EBS volume associated with that OpsWorks hostname.
Phrased in another way: data on an EBS is private to an instance and writes to that volume will not stomp on other instance's data.