How do I implement WCF-servers balancing

I have some business functionality implemented in WCF services that should be deployed on several workstations. Physically some workstations are placed in DataCenter "A" and some in DataCenter "B".

Clients should use business functionality without knowledge of how many workstations do I have and where do they placed.

There is no special requirements (up to now, but everything can change dramatically) how should we decide the workstation to serve cl开发者_开发技巧ient request (shall we take into account CPU load, total response time, failure history and so on)

At least there are several options how to implement ballancing:

One option I'm thinking about is to use two IIS Web Server facades (one for DataCenter "A" and one DataCenter "B") that delegate calls to workstations behind them. IIS facades should be joined into cluster with system network balancing.

Or may be I shall implement my WCF services to be hosted with IIS (I guess there should be problem to make them all visible to external clients)

Or may be I shall implement some sophisticated mediator service that analyze CPU load and workstation response time?