Each AWS Region supports the infrastructure and services for a given geography. Within each Region, Amazon builds isolated and redundant islands of infrastructure called Availability Zones (AZ).
With VMware Cloud on AWS, ESXi hosts traditionally reside in an AWS Availability Zone (AZ) and are protected by vSphere HA. In the event of losing a ESXi host in a cluster living on an AZ your VM will startup on a surviving host in the cluster.
The challenge is what happens if you lose your AZ? If you lose your AZ and are not replicating your data then you have a data unavailable event.
Stretched Clusters for VMware Cloud on AWS is designed to protect against an AWS availability zone failure.
Applications can span multiple AWS availability zones within a VMware Cloud on AWS cluster. vSAN Fault Domains are configured to inform vSphere and vCenter which Hosts reside in which Availability Zones. Each Fault domain is named after the AZ it resides within to increase clarity.
Consideration
This is a SDDC setting at point of creation. Make sure to perform proper due-diligence in your planning because you cannot create a stretched cluster after creation. In addition, once you create a stretched cluster you won’t be able to turn it into a regular cluster.
Configuring Stretched Clusters
Next you will choose your VPC you wish to use in your region.
Also, you will need to select 2 subnets which is a stretched cluster requirement.
Also, the witness host is also being deployed during this process outside the SDDC clusters
Now you are ready to log into the SDDC vCenter and start deploying VMs. DRS will honor the stretched cluster and it’s Fault Domains when it comes to placing VMs into your cluster.