Weblogic Interview Questions

Weblogic Interview Questions – 1

1)How do I provide user credentials for starting a server?

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.

2)Can I start a Managed Server if the Administration Server is unavailable?

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.

3)What is the function of T3 in WebLogic Server?

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.

4)How do you set the classpath?

WebLogic Server installs the following script that you can use to set the
classpath that a server requires:

WL_HOME\server\bin\setWLSEnv.cmd (on Windows)

WL_HOME/server/bin/setWLSEnv.sh (on UNIX)

5)How do stubs work in a WebLogic Server cluster?

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.

6)How does a server know when another server is unavailable?

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.

7)How are notifications made when a server is added to a cluster?

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.

8)How do clients handle DNS requests to failed servers?

If a server fails and DNS continues to send requests to the unavailable machine,
this can waste bandwidth. For a Java client application, this problem occurs
only during startup. WebLogic Server caches the DNS entries and removes the
unavailable ones, to prevent the client from accessing a failed server twice.

Failed servers can be more of a problem for browser-based clients, because they
always use DNS. To avoid unnecessary DNS requests with browser-based clients,
use a third-party load-balancer such as Resonate, BigIP, Alteon, and
LocalDirector. These products mask multiple DNS addresses as a single address.
They also provide more sophisticated load-balancing options than round-robin,
and they keep track of failed servers to avoid routing unnecessary requests.

9)How many WebLogic Servers can I have on a multi-cpu machine?

There are many possible configurations and each has its own advantages and
disadvantages. BEA WebLogic Server has no built-in limit for the number of
server instances that can reside in a cluster. Large, multi-processor servers
such as Sun Microsystems, Inc. Sun Enterprise 10000, therefore, can host very
large clusters or multiple clusters.

In most cases, WebLogic Server clusters scale best when deployed with one
WebLogic Server instance for every two CPUs. However, as with all capacity
planning, you should test the actual deployment with your target web
applications to determine the optimal number and distribution of server
instances.

10)How can I set deployment order for applications?

WebLogic Server allows you to select the load order for applications. WebLogic
Server deploys server-level resources (first JDBC and then JMS) before deploying
applications. Applications are deployed in this order: connectors, then EJBs,
then Web Applications. If the application is an EAR, the individual components
are loaded in the order in which they are declared in the application.xml
deployment descriptor.

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