I have installed ArcGIS Enterprise 10.5.1 with the automatic procedure of the Builder.
Everything went fine, all green checks.
I came up with having two working web adaptors, one for portal, one for server.
Everything is working when used from within the server where everything was installed.
The problem is the web adaptor took the FQDN of the server machine, so I was not able to sue it from another pc.
So I uninstalled and reinstalled both webadaptor pointing to a domain which is accessible from outside the server (and for which I have a SSL certificate for HTTPS connection).
I was then able to access portal and server from outside.
However, when I tried to logging in, a page with the Portal for ArcGIS layoutshowed up, but instead of the iframe to insert my credentials, I got a 404 error page.
Everything seems caused by the fact that during login, the authorization goes through the Portal and the URL somehow is still set to the FQDN, causing the request to time out (becasue, again, it is not recognized from outside the server).
I have changed the tier from ARCGIS_PORTAL to GIS_SERVER in the server administratrion page.
I was then able to login but then then I had issues with validating the federated server.
I would need to have the server federated with the portal because I would need to publish services to it from ArcGIS Pro.
How can I overcome the problem of the FQDN/EXTERNAL DOMAIN?
Should I give up using the Builder and do a clean install from scratch by soing thins manually?
Also, if you want to see what I have already been trying, please refer to this other thread.