It shouldn't matter which XenApp servers host the applications. As long as it's just one Citrix cluster, the XMLBrokers will serve the request for them.
The sequence is that the client makes an XML request to the XMLBroker. Which then responds with the information telling the client which XenApp server to connect to. the client then connects directly to the XenApp server and doesn't need to talk to the XMLBroker any more.
[The XMLbrokers are literally just that. Brokers. The XenApp servers tell the broker which apps they're willing to serve and the Broker tells the clients that. And then when you start an app, the client says to the broker - Start me Up - the broker then 'arranges' the running of the app and returns the information as to where it is running]
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