Portal, after it is installed, is not accessible from public IP in AWS. Hence, installing Web Adaptor is necessary to make it accessible from public IP.
The installation guide refers Setup program but it doesn't exist in AWS Marketplace image. You can find /arcgis/webadaptor10.7.1/.Setup directory though.
System requirement says Tomcat 9.0.19 but Ubuntu installs Tomcat 9.0.16 via apt.
If you call web page with public IP / DNS, lynx http://arcgis-server.gisdemo.net:8080/arcgis/webadaptor, you get the following 999 error:
The web adaptor configuration URL has to be accessed from the machine hosting the web adaptor.
If you call web page with internal IP, $lynx http://172.31.49.200:8080/arcgis/webadaptor, you get the following 400 error:
Unable to configure the ArcGIS Server with the Web Adaptor. Please make sure that the server machine is running and that the account specified has administrative privileges to the site.
If you use CLI tool configurewebadaptor.sh, it cannot access web adaptor URL:
(base) arcgis@ip-172-31-49-200:/arcgis/webadaptor10.7.1/java/tools$ /arcgis/webadaptor10.7.1/java/.Setup/jre/bin/java -jar /arcgis/webadaptor10.7.1/java/tools/arcgis-wareg.jar -m portal -w http://172.31.49.200:8080/arcgis/webadaptor -g https://172.31.49.200:7443/arcgis -u siteadmin -p password -a true Unable to connect to WebAdaptor URL : http://172.31.49.200:8080/arcgis/webadaptor