How to see updates to EBS volume when attached to multiple instances?

Solution 1:

You'll need a filesystem / app that's multi-attach aware. For example Oracle RAC can use such volumes, while normal filesystems like ext4 or xfs can't. They are designed to be mounted on a single host only.

Let's step back - what are you trying to achieve? Share files between the instances I suppose? Your best bet is EFS (Elastic File System) - an AWS cloud-native NFS service. Unless you've got a very specific need for multi-attach EBS and running some very special app that can make use of that I suggest you explore the EFS way instead. The need for multi-attach disks is rare, both in the cloud and outside.

Hope that helps :)