1)Question :How are notifications made when a server is added to a cluster? 

Answer :The WebLogic Server cluster broadcasts the availability of a new server instance each time a new instance joins the cluster. Cluster-aware stubs also periodically update their list of available server instances.


2)Question :How does a server know when another server is unavailable? 


Answer :WebLogic Server uses two mechanisms to determine if a given server instance is unavailable.

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. The other server instances will drop a server instance from the cluster, if they do not receive three consecutive heartbeats from that server instance

WebLogic Server also monitors socket errors to determine the availability of a server instance. For example, if server instance A has an open socket to server instance B, and the socket unexpectedly closes, server A assumes that server B is offline. 

3)Question :How do stubs work in a WebLogic Server cluster? 

Answer :Clients that connect to a WebLogic Server cluster and look up a clustered object obtain a replica-aware stub for the object. This stub contains the list of available server instances that host implementations of the object. The stub also contains the load balancing logic for distributing the load among its host servers.

What happens when a failure occurs and the stub cannot connect to a WebLogic Server instance?
When the failure occurs, the stub removes the failed server instance from its list. If there are no servers left in its list, the stubb uses DNS again to find a running server and obtain a current list of running instances. Also, the stub periodically refreshes its list of available server instances in the cluster; this allows the stub to take advantage of new servers as they are added to the cluster. 

4) Question : How do I provide user credentials for starting a server  

Answer :When you create a domain, the Configuration Wizard prompts you to provide the username and password for an initial administrative user. If you create the domain in development mode, the wizard saves the username and encrypted password in a boot identity file. A WebLogic Server instance can refer to a boot identity file during its startup process. If a server instance does not find such a file, it prompts you to enter credentials.
If you create a domain in production mode, or if you want to change user credentials in an existing boot identity file, you can create a new boot identity file. 


5)Question :How do you set the classpath? 

Answer :WebLogic Server installs the following script that you can use to set the classpath that a server requires:
WL_HOMEserverinsetWLSEnv.cmd (on Windows)
WL_HOME/server/bin/setWLSEnv.sh (on UNIX) 


Question : What is the function of T3 in WebLogic Server?  

Answer : T3 provides a framework for WebLogic Server messages that support for enhancements. These enhancements include abbreviations and features, such as object replacement, that work in the context of WebLogic Server clusters and HTTP and other product tunneling. T3 predates Java Object Serialization and RMI, while closely tracking and leveraging these specifications. T3 is a superset of Java Object. Serialization or RMI; anything you can do in Java Object Serialization and RMI can be done over T3. T3 is mandated between WebLogic Servers and between programmatic clients and a WebLogic Server cluster. HTTP and IIOP are optional protocols that can be used to communicate between other processes and WebLogic Server. It depends on what you want to do. For example, when you want to communicate between a browser and WebLogic Server-use HTTP, or an ORB and WebLogic Server-IIOP.  



Question : Can I start a Managed Server if the Administration Server is unavailable? 
 

Answer : By default, if a Managed Server is unable to connect to the specified Administration Server during startup, it can retrieve its configuration by reading a configuration file and other files directly. You cannot change the server's configuration until the Administration Server is available. A Managed Server that starts in this way is running in Managed Server Independence mode.


Question : How do I enable debugging for the messaging bridge?  

Answer : You can enable debugging for the messaging bridge using either of the followings methods:

* Add the following lines to your WebLogic start script (before the weblogic.Server line):

-Dweblogic.debug.DebugMessagingBridgeStartup=true

-Dweblogic.debug.DebugMessagingBridgeRuntime=true

* Add the following statements to the ServerDebug entry in your configuration file (config.xml) for the server that the messaging bridge is running on:

DebugMessagingBridgeStartup="true"

DebugMessagingBridgeRuntime="true"

Once debugging is enabled for the messaging bridge, the debugging messages are sent to the server log by default. However, if you want them to appear in the Administration Console, add “DumpToConsole” to the statements show above. For example:

-Dweblogic.debug.DebugMessagingBridgeStartupDumpToConsole=true