A. Clusters provide clients with transparent failover.
B. EJB applications can be targeted to an entire cluster.
C. All cluster members must bind to the same port number.
A: If an object is clustered, failover and load balancing for that object is available. In a WebLogic Server cluster, application processing can continue when a server instance fails. You "cluster" application components by deploying them on multiple server instances in the cluster--so, if a server instance on which a component is running fails, another server instance on which that component is deployed can continue application processing.
The choice to cluster WebLogic Server instances is transparent to application developers and clients.
B: A clustered application or application component is one that is available on multiple WebLogic Server instances in a cluster. If an object is clustered, failover and load balancing for that object is available. Deploy objects homogeneously--to every server instance in your cluster --to simplify cluster administration, maintenance, and troubleshooting.
Web applications can consist of different types of objects, including Enterprise Java Beans (EJBs), servlets, and Java Server Pages (JSPs).
Note: Load balancing and failover for EJBs and RMI objects is handled using replica-aware stubs, which can locate instances of the object throughout the cluster.
C: Cluster Multicast Address and Port
Identify the address and port you will dedicate to multicast communications for your cluster.
Incorrect answers:
D: Cluster heartbeats-- Each WebLogic Server instance in a cluster uses multicast to broadcast regular "heartbeat" messages that advertise its availability. By monitoring heartbeat messages, server instances in a cluster determine when a server instance has failed.
E: All server instances in a cluster must reside in the same domain; you cannot "split" a cluster over multiple domains. Similarly, you cannot share a configured resource or subsystem between domains.
F: Proxy might be needed depending how you set up the architecture, but a proxy is not required for web applications.
Reference: Using WebLogic Server Clusters , Understanding WebLogic Server Clustering