Question about system-reboot

When AWS schedules a system-reboot for your EC2 instance, here's what you can expect:

1. Regarding the duration: The 2-hour window is the maximum time allocated for the maintenance, but the actual downtime for your instance will likely be much shorter. During a system-reboot, your instance is migrated to a new host, which typically completes in minutes rather than hours. AWS reserves the full window to provide flexibility across many instances, but you should be able to use your instance well before the end of the 2-hour period in most cases.

2. Regarding instance changes: During a system-reboot, your instance will be migrated to a new host. While your instance retains its IP address, DNS name, and data on instance store volumes, the underlying physical hardware will change. This is important for your SAP application's license manager that's tied to a hardware key. Since the hardware key is derived from the physical host, a system-reboot that migrates your instance to new hardware will likely change this key, which could affect your SAP licensing.

If your SAP license is tied to a hardware key, you should contact your SAP representative before the scheduled maintenance to understand the implications and prepare accordingly. You might need to reactivate your license after the system-reboot is complete.
Sources
Will my EC2 instance lose its public IP during scheduled system-reboot maintenance? | AWS re:Post
Manage Amazon EC2 instances scheduled for reboot - Amazon Elastic Compute Cloud
Reboot your Amazon EC2 instance - Amazon Elastic Compute Cloud