We have a military client deploying an application that uses a print GP task published from the standard ArcGIS print task (based on the custom print task tutorial). On our developer system (not in military network), the print task works fine. But on the client's system, the print task fails when using the Web Adaptor. We can temporarily configure it to use the internal URL (port 6443) and it will work on a test machine, but they cannot use the internal URL for production. This is using ArcGIS Server 10.3 on a Windows Server 2008/IIS7 environment. IIS is on a separate machine from the GIS server.
The problem is that the full URL to the ExportWebMap task does not work when going through the Web Adaptor. Using a browser on their network, they can access the basic print service in the Services Directory, along the lines of http://servername.army.mil/arcgis/rest/services/myprintservice/GPServer. But if they click on the Export Web Map link, they get an error message (see also attached graphic):
Could not access any GIS Server machines. Please contact your system administrator.
At first I suspected an IIS issue, but the request is obviously reaching the Web Adaptor. Any idea why the print task itself would not get forwarded to the GIS server? My guess is it has something to do with spaces in the task name, but it's odd that this would work on our developer network but not on the client network.
When we use our custom GP print task on a machine that is not the ArcGis Server where the service is running, we had to create an empty proxy file one the "remote" web server.
i apologize that I am not at a location to provide a sample of the text right now.