failover onto an applications server

Backgroud
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Client wants to implement fail-over in it's SAP Production server (database + SAP). Users login to either the DB server or the application server to spread the load, the appliaction server references the DB server. On the case where the DB server failed, the application server will stopsap and take over the database from the DB server.
The servers have different names and IP addresses

Questions:
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1. What are needed for the cluster implementation?
2. What are the watchouts?
3. The implementation procedures, if any?
4. If not, any directions or suggestions?

Thank you very much.