The topologies included in conf/topologies include hostmap provider config with a comment that needs some work (IMO).
"Defines rules for mapping host names internal to a Hadoop cluster to externally accessible host names. For example, a hadoop service running in AWS may return a response that includes URLs containing the some AWS internal host name. If the client needs to make a subsequent request to the host identified in those URLs they need to be mapped to external host names that the client Knox can use to connect.
If the external hostname and internal host names are same turn of this provider by setting the value of enabled parameter as false.
The name parameter specifies the external host names in a comma separated list.
The value parameter specifies corresponding internal host names in a comma separated list."
Note that when you are using Sandbox, the external hostname needs to be localhost, as seen in out of box sandbox.xml. This is because Sandbox uses port mapping to allow clients to connect to the Hadoop services using localhost. In real clusters, external host names would almost never be localhost."