I wonder if we can configure ArcGIS for server or Portal with Web Adaptor installed in different machine. I went through different blogs reaching to a conclusion that we can configure with web adaptor in the same machine.
If your Web-Server machine is different from ArcGIS Server machine, then the web-adaptor should be installed in the web-server machine. The web-server and ArcGIS server should be able to communicate with each other.
Configuring ArcGIS Web Adaptor after installation—Installation Guides (10.3 and 10.3.1) | ArcGIS for Server
You can install it where ever you like.. as long as it can communicate with your ArcGIS Server, or Portal or both. (depending on application use).
It is good practice to install it on the WEB APP Server, where the applications reside (IIS).
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