EC2 Scope in Amazon Web Services
Elastic Compute Cloud (EC2) images and instances contained within Amazon Web Services (AWS) regions, which can create a challenge if you want your instances to be able to run in multiple regions. Now, why would you want your instances to run in multiple regions? Here are some reasons:
As protection against failure in an AWS availability zone (AZ) or region: If AWS suffered an outage in one portion of its service area, you can continue to operate your application in another availability zone or region.
To reduce latency when serving users located in specific geographic regions: By placing instances in, say, the Australia-based Asia Pacific region, you would reduce overall network transit time to users located nearby.
So that you can operate a multiregion application to ensure the best possible performance to a user base spread throughout the world: In addition to the need to manage images in multiple locations, you may take advantage of two other AWS services:
Route 53: Amazon's distributed DNS service
CloudFront: Amazon's S3-based content delivery network
To comply with national requirements for data privacy: Some countries impose restrictions on the locations where data related to their citizens or businesses resides. You may choose to run your application in multiple regions to comply with these restrictions.
EBS-backed images can be launched in any availability zone within the region where the image resides; this is different from the general EBS scoping limitation, which restricts the use of an EBS volume to the availability zone in which it's located.