40 Important Weblogic Interview questions

Here is the compilation of 40 Important Weblogic Interview questions

Question 1:
What is a WebLogic server?
Answer
Oracle WebLogic Server is J2EE Server (earlier known as BEA WebLogic Server) similar to  Oracle Application Server.
Oracle Weblogic server

Question 2:
What oracle WebLogic server includes?
Answer
Oracle WebLogic server includes

(1)Domain
(2)cluster
(3)servers

Question 3:
We often see BSU when using WebLogic. What is the meaning of BSU?
Answer
Oracle bought Weblogic from BEA. BSU Stands for Bea Smart Update.  This utility is used to apply the WebLogic Server Patches. In simple terms, it is the first letter of the name of founders  Bill Coleman, Ed Scott, and Alfred Chuang.

Question 4:
What is a domain in WebLogic?
Answer
The domain is a group of WebLogic server resources like admin server, managed server, JMS, connection pool, data sources, etc or whatever the resource you know of WebLogic server.  since the domain is the basic unit you have to create after installation and everything created and configured under a domain. There can only be one administration Server in the domain and zero to N Managed Server.

How to create WebLogic Domain

Question 5:
What is Administration Server?
Answer
Admin server is the central point from where you can configure, monitor, and manage all resources of a domain.
Administration Server is a WebLogic Server instance that maintains configuration data for a  domain. You can deploy your application on the administration Server but it is recommended to create managed Server and deploy your application in managed server and leave the Administration domain for configuration and maintenance.
There will always be at least one Administration Server in a domain.

How to stop-start the Weblogic server

Question 6:
What is Managed Server?
Answer
It is an instance of your WebLogic server that is running on JVM and has its own configuration.
In Managed server, we will deploy the java components
Web Applications
EJB Applications
JMS Applications
Web services
How to stop/start the Managed server

Question 7:
Can we 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 8:
What is the easiest way to set the classpath?
Answer
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)
where WL_HOME is the directory in which you installed WebLogic Server

Question 9: 
What is Cluster in WebLogic?
Answer
Two or more managed server becomes or forms the cluster in a domain and the cluster handle the load balancing across the cluster.
Group of WebLogic Managed Server Instances that work together to provide high availability and scalability for applications is called a cluster. WebLogic Servers within a cluster can run on the same machine or different machines. These are also called managed Server clusters.

Question 10:
What is Server
Answer
The server is an instance of your WebLogic which is running on a JVM and has dedicated RAM.

Question 11:
How to start Node Manager?
Answer

$WL_HOME\server\bin\startNodeManager.sh

To Stop Node Manager
In Unix/Linux, kill the process –

kill -9 ps -ef | grep -i nodemanager.javahome | grep -v grep | awk {'print $2'} | head -1

How to start/stop Node manager

Question 12:
Why node manager is required?
Answer
A Node Manager process is not associated with a specific WebLogic domain but with a  machine. You can use the same Node Manager process to control server instances in any WebLogic  Server domain, as long as the server instances reside on the same machine as the Node  Manager process. Node Manager must run on each computer that hosts WebLogic Server instances. whether Administration Server or Managed Server that you want to control with  Node Manager.
Question 13:
How many types of Weblogic installation?
Answer
There are 3 types of WebLogic installation.
(a) Graphical Mode (interactive GUI based)
(b) Console Mode (interactive Text Based)
(c) Silent Mode ( Non Interactive method using .xml properties file)
How to perform the weblogic Installation

Question 14:
How does Cluster Communication Happen?
Answer
Members of the Cluster communicate over the Cluster Multicast IP and Port by sending periodic heartbeat messages.

Question 15:
What is the difference between the Sun JVM and BEA JRockit JVM?

Answer

The Sun Java Virtual Machine (JVM)  is called HotSpot. it is shipped in the Java Developer’s Kit (JDK) and Java Runtime Environment (JRE)  from Sun. It is well suited for various applications and performs well. A lot of development efforts is being put in to make it better each day

The BEA JRockit JVM from BEA systems is highly optimized for reliability and performance for server-side applications. JRockit JVM uses technologies such as code generation, hot spot detection(the methods that are being run more often), code optimization, advanced garbage collection algorithms, and tight operating system integration for faster performance.

In Hotspot byte code is read and translated into machine language, but these results are not saved in the memory while in JRockit the byte code is translated to machine language and this is saved in the memory. so if the method is run again, there is no need for translation, and the machine code is reused and we get faster performance

Now both Hotspot and Jrocket are owned by oracle   and things will definitely change for these in future

Weblogic: Sun JDK and Oracle Jrocket

Question 16: 

What are JVM Tuning Parameters?
Answer
If you have a single processor, the single-thread machine then you should use the serial collector (default for some configurations, can be enabled explicitly for with -XX: +UseSerialGC). For multiprocessor machines where your workload is basically CPU bound, use the parallel collector. This is enabled by default if you use the -server flag or you can enable it explicitly with -XX:+UseParallelGC. If you’d rather keep the GC pauses shorter at the expense of using more total CPU time for GC, and you have more than one CPU, you can use the concurrent collector (-XX:+UseConcMarkSweepGC).

Question 17:
How do you do performance tuning of WLS? What are various areas to  do it
Answer
a. Application Tuning.
JSP precompilation, EJB pool size cache.

b. OS Tuning
Setting TCP IP parameter.
tcp_time_wait_interval
tcp_conn_req_max_q

c. Core Server Tuning.
tune work manager, tune chuck size and chunk pool size, using performance packs,  connection backlog buffering.

d. JVM Tuning
tuning GC strategy, monitoring garbage collection.

Question 18:

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

Question 19:

What is HTTP tunneling? How can we configure it on WebLogic?
Answer
HTTP tuning provides a way to simulate a tasteful socket connection between WebLogic  Server and a Java client when your only option is to use the HTTP protocol.
It is generally used to tunnel through an HTTP port in a security firewall. HTTP is a stateless protocol, but WebLogic Server provides tunneling functionality to make the connection appear to be a regular T3 Connection.
Steps to configure HTTP tunneling.
a)Login into the Admin Console, click on the server on which you want to enable the HTTP Tunneling feature
b)Click on the Protocols tab
c)General
d)check the “Enable Tunneling” check box.
e)Now you can communicate with the JVMs (Server Instances) using protocols other than t3

Question 20:

What is the difference between T3 and HTTP protocols?
Answer
WebLogic uses the T3 protocols for internal and external connections to the servers. The  T3 protocol often is used in the WebLogic implementation of RMI. It is Proprietary to WebLogic  Server.

A Weblogic server instance keeps track of each Java Virtual Machine (JVM) with which it connects, and creates a single T3 connection to carry all traffic for a JVM.

HTTP protocols are used primarily for HTTP communication between the browser and the webserver. Standard follows the W3C (World Wide Web Consortium).Note: All of these protocols are, by default, multiplexed over the same connection to the server’s address and port. So you can access a web page hosted by the server using a URL  such as http://host:port/page.jsp.

An external client can set up an initial JNDI context to a server using the URL t3://host: port/. All that has changed is the protocol over which the client must communicate with the server.

Question 21:
What are the  States of the Weblogic Server?
Answer
There are 9 states of server which are given below
Shutdown
Starting
Standby
Resuming
Running
Suspending
Shutting down
Failed
Unknown

Question 22:
What is the difference between Multicast and Unicast?

Answer

Unicast is the method used in the clustering technique where there is a cluster master and each server should ping to this cluster master for informing that the server is alive.

Multicast: It is a kind of clustering system where there is no cluster master and each and every server needs to ping each other for informing their existence. Multicasting has many messages to be sent in the form of ping as each server needs to inform all others about its existence. This condition creates much complexity associated with the method compared to unicast.

Question 23:
How to access the admin console?
Answer
ssl enabled admin console accessed as :
https://<hostname_or_ip_address_where_admin_server_running>:<port_on_which_admin_server_is _running>/console
Example – https://localhost:7002/console

non ssl admin console accessed as :

http://<hostname_or_ip_address_where_admin_server_running>:<port_on_which_admin_server_is_ running>/console
Example – http://localhost:7001/console

Question 24:
How many admin consoles are possible in a single domain?
Answer
only one is possible

Question 25:
What is the default port of the admin server?
Answer
7001

Question 26:
What is config.xml in the WebLogic server?
Answer
config.xml is the central configuration repository for a domain. every resource you have configured from the admin console or by command line or by any other tool registered under this file.

Question 27:
What is boot.properties file? what is the significance of it
Answer
boot. properties is the file used by the admin or managed server during startup for username and password. it exist under your domain/servers/server_name/security folder.
When you create a domain in development mode then it creates automatically during the startup of the admin server but if you create a domain in production mode then you need to define it explicitly otherwise on every reboot of the admin server it will prompt you for username and password.
So in production mode –
Start admin server by manually passing the username and password
stop it ( press cntrl+c on the started session )
go to your domain/servers/your_admin_server/  create a folder “security”
go inside security and create a file “boot. properties” with below contents
username=your_admin_username
password=your_admin_password
now start the admin server, it will not prompt you for username & password further.
If you are going to start your managed servers from the admin console then no need to create  this file for the managed server but if you are going to start managed servers via the startManagedweblogic script then you need to follow the same above procedure for each
managed server.

Question 28:
What is actually WebLogic Cache?
Answer
Basically, all the web-tier related files (.jsp .class, JSPCompiled files, etc.,) get stored in some directory. This is treated as cache whenever there is a restart of a WebLogic instance happen then the WebLogic server will lookup for the last serviced object status stored in the cache to service for any pending requests. Usually, when your EJB Classes need sessions, the JMS object requires persistence, your web-tier may contain static contents then Cache will be used by WebLogic Application Server instance.

Question 29:
Why do we need to remove Cache?
Answer
Whenever your application is accessed for the first time that fresh deployment of a new version, WebLogic server lookup in this directory if there are older objects persists that will be a conflict with new code objects. This is where the need for the removal of cache arises. Where there is a need for a new version deployment we might need to clear the cache when the changes to the new version are not reflected.

Generally for WebLogic 9. x and higher versions
WIN: C:\weblogic\user_projects\domains\yourdomain\servers\yourserver\tmp
UNIX: /weblogic/user_projects/domains/yourdomain/servers/yourserver/tmp

you can use the following commands to clear the cache:
WIN: rd C:\weblogic\user_projects\domains\yourdomain\servers\yourserver\tmp
UNIX: rm -rf /weblogic/user_projects/domains/yourdomain/servers/yourserver/tmp

Here I am removing all the subdirectories and files in the the given directory.

Question 30:
What is a Thread dump?
Answer
Thread Dump is a textual dump of all active threads and monitors of Java apps running in a
Virtual Machine.

Question 31:
When we will take the Thread dump? Please give us some examples
Answer
Some of the examples would be
1.  when the server is hung Position, i.e. that time server will not respond to coming requests.
2. While sever is taking more time to restart
3. When we are Getting exceptions like “java. lang.OutOfMemoryException”
4. Process running out of File descriptors. The server cannot accept further  requests because sockets cannot be created
5. Infinite Looping in the code

Question 32:
How many ways take Thread Dumps?
Answer
we have to take Thread dumps many times when we faced issues. We can choose one  Procedure. For analyzing take dumps some Intervals (like every 20mins, 5mins, etc.).

Question 33:
What you Can Do with Node Manager
Answer
We can manage the whole gamut of activities from the Node manager
1) Start, Shut Down, and Restart an Administration Server
2) Start, Shut Down, Suspend, and Restart Managed Servers
3) Monitor Servers and View Log Data

Question 34:
How to check port number?
Answer
netstat -na |grep connected (to find the ports connected in Linux box.)
netstat -na |grep listen (to find the listening ports in HP-UX,Solaris)

Question 35:
What are the capabilities of the WebLogic servers?
Answer
There are various capabilities associated with the WebLogic server and they are
Changes in dynamic configuration.
Production application redeployment
Rolling upgrades.

Question 36:
How can default JVM be changed to another?
Answer
Changing the JVM can be done by following the steps below.
1)You should first set the JAVA_HOME in the start script of the server.
2)Change the config.xml of the domain for using the JRockit javac.exe
3) Remove any kind of switches specific to Sun JVM from the start scripts of the server.

Question 37:
What are the modes of operation for Weblogic server domains?
Answer
There are two modes
Development mode:
You use development mode while you are developing your applications. Development mode uses a relaxed security configuration and enables you to auto-deploy applications.
Production mode:
You use production mode when your application is running in its final form. A production domain uses full security and may use clusters or other advanced features.

Question 38:
We see errors like  404 and 500. What do they mean?
Answer
The error code 404 – Page not found this says there is no page on the server when browser client requesting, this can happen when the application is not deployed properly or not in active state or not initialized properly
500- Internal server error This error occurs when there is a communication issue between the server’s intermediate services

Question 39: 
What is the difference between stage and no stage deployment?
Answer
Stage Deployment:- Admin server Having the physical copy and will distribute to remaining instances.
The staged deployment will copy your deployment units onto the deployment servers, place them into the $WL_HOME/servers/SERVER_NAME/stage directory and deploy them from there.

In no-stage mode, the Administration Server does not copy the archive files from their source location. Instead, each target server must access the archive files from a single source directory for deployment.

The staging directory of target servers is ignored for no-stage deployments.

Question 40:
how to check the version of java in Unix?
Answer
java -version run this command in Linux to know the java version.

I hope you like the compilation of Weblogic Interview questions.

Here is a nice Udemy course for review for Weblogic 12c
Oracle weblogic 12c for administrator
How to secure Oracle Weblogic 12c

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