web.config file of DXA you can specify a
cid-localhost setting. This setting is commented as follows:
Use the setting below if you need to map localhost to a specific hostname so the CID service can access resources. On some environments localhost may not resolve correctly to the external hostname.
I don't understand why you would need to map localhost to something else. Why does the CID service need to access resources on the application server? Surely it just returns the requested binaries? Or is there more to it?
How does this setting get used? When would you configure it, and what value would it make sense to use?