We have a federated ArcGIS Enterprise which is accessible through our Intranet. After a while we decided to add another WebContext-URL to the site with a reverse proxy to let our ArcGIS Enterprise be although accessible trough the Internet. Unfortunately we found out that this is not possible anymore after the Federation. We would appreciate it very much if this would be doable without unfederating the ArcGIS Enterprise because it was already productive. Thought that this would be a default configuration option, that's why probably some more users were confronted with that issue. Someone maybe found a workaround? Any Update whether it's going to be possible in the next release?
If the URL that you've used when federating Portal and Server uses a DNS alias rather than a machine name, then could you look potentially look at having this as an external DNS pointing to the reverse proxy. This should work provided that internal users always hit the internal DNS and external users hit the external DNS. I've seen this setup with both Citrix NetScaler and Apache, although I haven't configured the proxies myself so can't offer much insight into the settings, content switching rules etc.
The only way that you could change the Portal owning URL is to un-federate and re-federate. This is the URL that was used to create the federation.
But, if you just want to change the service URL in the federation to allow the client to be able to pull the services with the new URL follow these steps.
Access the Portal sharing endpoint=> login=> home=> portal=> self=> servers=> click on the federation and update the service URL to the new URL.