Using ArcGIS Server 10.2.1, we deployed our publicly open internet site using two different IIS servers - each with a Web Adaptor - and a single ArcGIS Server behind a firewall. The incoming requests are managed by a load balancer that sends them to either one of the IIS servers.
Our Web Adaptors are named "arcgis" and "arcgis2", and our REST services library is in the form of site.domain/arcgis/rest/services and site.domain/arcgis2/rest/services.
Something doesn't work as expected. Both IIS servers are up, but when we are trying to reach them we get a 404 error for one while the other works fine. A few minutes later they switch, and we get a 404 error for the previously working Adaptor, while the former 404 Adaptor now works fine. This repeats itself continuously.
As a result we have difficulties with consuming our REST services (for example, in ArcGIS Online).
What can I check to find where is the problem?