The sources.hosts setting in the Waveset.properties file controls which hosts in a multi instance environment are used for executing Active Sync requests. This setting provides a list of hosts that source adapters can run on. Setting this to localhost or null will allow source adapters to execute on any host in the web farm. (This is the default behavior.) By listing one or more hosts, you can restrict execution to that list. If you have inbound updates from another system that go to a particular host, use the sources.hosts setting to record the host names.
In addition, you can define a property named sources.resourceName.hosts, which controls where the resource's Active Sync task will run. Replace resourceName with the name of the resource object you wish to specify.