Two Instances On Same Node In Clustering

Need some advice .


Our management want to have two instances of SQL Server 2005 in Clustered environment.


First instance will serve existing application and Second instance will serve their new application.


As Microsoft suggests that, its not a good practice to have multiple instance on the same node, until you have any compelling reason to have such setup. The compelling reason what the mangement have is , some time ago they used same instance for both the application. What happened was, the secondary application took all the resources from primary(main) application, and server went down( this was past.).


So, now in clustering they want to have their first instance (which will serve our existing application) with enough CPU cores & memory so that it can run smoothly and then have second instance with the remaining CPU power & memory. So ,in case if second instance tries to eats up all the resources, it can eat what it have , it cannot take resources from primary instance.


But, what my idea here is:

Initially, dont install second instance for new application( in clustering environment). Instead ,use existing servers for the upcoming new appication where production & DR is there right now ( Standalone servers).


What i mean here is: After making sure that the existing (Primary) application is comfortable in clustering environment (in PRODUCTION) , until then, run the second application on the old PROD box & old DR will serve as its DR. So ,by going in this way , we are not installing initally two instances on the same node. When the life is good for the first instance, then based on those results, we can think for the second instance.


Ii wanted to know from you guys, what you think about this. Is this idea look feasible. Please let me know.


Thanks for reading all this