User 'siteadmin' cannot access the ArcGIS Server administration URL 'https://fqn.domain.com/server'

Error Message

When trying to federate ArcGIS Server with Portal for ArcGIS, the federation failed with the following error:

 User 'siteadmin' cannot access the ArcGIS Server administration URL 'https://fqn.domain.com/server'

The deployment was a single machine base deployment, hence accessibility/network issues were ruled out.

Cause

N/A

Solution or Workaround

1. Sign in to the machine on which ArcGIS Server is installed. 
2. Browse to the following folder:

<Server installation directory>\framework\etc

3. Create a file named hostname.properties, with appropriate permissions, in this folder.
4. Add the following text to the first line of the file, and specify the fully qualified domain name of the intended interface:

hostname=interface.domain.com

5. Save and close the hostname.properties file.
6. Restart the ArcGIS Server service on Windows.