While your company might operate in multiple regions, one region should typically be selected as the primary region. Certain resources will not be geographically distributed, and these should be provisioned in this default region.
When building out your AWS infrastructure from scratch, it's a good time to revisit decisions that might have been made decades ago. Many new AWS regions might be better suited for the business.
Customer Proximity
One good option is picking a default region that is closest to where the majority of end-users reside.
Business Headquarters
Frequently we see the default region selected that is closest to where the majority of business operations take place. This is especially true if most of the services in the default region will be consumed by the business itself.
Stability
When operating on AWS, selecting a region other than us-east-1 is advisable as this is the default region (or used to be) for most AWS users. It has historically had the most service interruptions presumably because it is one of the most heavily-used regions and operates at a scale much larger than other AWS regions. Therefore we advise using us-east-2 over us-east-1 and the latencies between these regions are very minimal.
High Availability / Availability Zones
Not all AWS regions support the same number of availability zones. Many regions only offer (2) availability zones when a minimum of (3) is recommended when operating kubernetes to avoid “split-brain” problems.
Cost
Not all regions cost the same to operate. On the other hand, if you have significant resources deployed in an existing region, migrating to a new region could be cost-prohibitive; data transfer costs are not cheap, and petabyte-scale S3 buckets would be costly to migrate.
Service Availability
Not all regions offer the full suite of AWS services or receive new services at the same rate as others. The newest regions frequently lack many of the newer services. Other times, certain regions receive platform infrastructure updates slower than others. Also, AWS now offers Local Zones (e.g. us-west-2-lax-1a) which operate a subset of AWS services.
Instance Types
Not all instance types are available in all regions
Latency
The latency between infrastructure across regions could be a factor. See cloudping.co/grid for more information.