On this page you will find cluster configurations that provide ways you can help setup your quorum/witness alongside existing nodes within an AWS cloud environment.
Key for diagrams below:
If both nodes all reside in the same region, then the witness node should reside in same region. If any availability zone in the region fails, you still have one node and a witness node. If the entire region fails you have no nodes anyway, so failover becomes irrelevant.
In a 3-node cluster where two nodes live in one region and the 3rd lives in a different region then a witness node does not need to be added to the cluster. This is because we already have an odd number of votes. Failover to the DR region will always be a manual process in the event of the failover of the entirety of region 1.
In a 2-node cluster where one node lives in region 1 and node 2 lives in region 2, the witness should reside in region 3 if you have it, but region 1 if you don’t have it. The reason to not put it in region 2 is that a failure of the network between region 1 and region 2 will cause a failover to region 2 unnecessarily. Having a 3rd region eliminates that possibility. If the 3rd region in not practical, then putting it in the primary region is preferable to eliminate false failover. However, in the event of a complete failure of region 1, you will have to bring the secondary server online manually. When this event occurs, please be sure to log the time/date of the failure and specifically what was done to bring the server online.
Amazon S3 buckets are accessible globally. NFS or EFS could be set up in the same region.