what is the best practice for weblogic in terms of creation of instance. Suppose I have 10 applications which are independent but can be grouped in 3 bunch. So whether all should go under once instance or more than one instance is advisable.
Start with 1 if you can run all 10 apps on 1 instance and your apps are not going to handle much load.
But you still have to do your homework to plan your infrastructure properly. For instance, you may need more than 1 physical server due to network topology, you may need a cluster with many instances simply due to the amount of load your applications may need to handle (or you may have strict HA requirements), you may need different domains because your apps require different versions of the app server, etc.