In the cloud everything can happen. Actually, everything will happen.
Therefore, in your design, you should be ready for failures: even if you expect your disk mounts to be there for you, they might not be. And you are doing auto-scaling, it is most likely that at some time they won't be there for you.
Therefore, to avoid hanging servers due to failure to mount disks and bad messages such as: "The disk drive for /tmp is not ready yet or not present," make sure your servers are not bound by your disks; otherwise, you will not be able to contact your servers, or your OpsWorks will notify you that the server is booting forever.
Avoid Waiting for Your Mount
The secret is a small option: nobootwait that will make sure your server is not waiting for the mount to be ready. You can configure it in your /etc/fstab, or even better in your Chef recipe:
mount "/tmp" do device "184.108.40.206:/tmp" fstype "nfs" options "rw,nobootwait" action [:mount, :enable] end
The right design will help you keep you system running in a cloud-based environment.