EFS and EC2 instance

Hello.

Even if the Availability Zone is different between EC2 and EFS, it is possible to mount and use it.
If the Availability Zones are different, please note that communication costs will be incurred as communication will be between Availability Zones.
https://docs.aws.amazon.com/efs/latest/ug/accessing-fs.html

The following diagram shows an Amazon EFS file system that's using One Zone storage classes, with a single mount target created in the same Availability Zone as the file system. Accessing the file system by using the EC2 instance in the us-west2c Availability Zone incurs data access charges because it is located in a different Availability Zone than the mount target.