This template will provision a highly available web GIS deployment on two AWS instances plus one instance for a file server. A web GIS deployment includes Portal for ArcGIS, ArcGIS Server, ArcGIS Data Store, and ArcGIS Web Adaptor. It will set up an architecture as shown in the graphic below.
WebGIS.esri.com
to arcgis-WebGISha-123456789.us-east-1.elb.amazonaws.com
through CNAME mapping.
See Troubleshoot AWS CloudFormation stack creation in the ArcGIS Server on Amazon Web Services help if you run into problems.