Oracle Apps DBA Weblogic Interview Questions and Answers

1. What is BEA Weblogic?
BEA WebLogic is a J2EE application server and also an HTTP web server by BEA Systems of San Jose, California, for Unix, Linux, Microsoft Windows, and other platforms. WebLogic supports Oracle, DB2, Microsoft SQL Server, and other JDBC-compliant databases. WebLogic Server supports WS-Security and is compliant with J2EE 1.3. BEA WebLogic Server is part of the BEA WebLogic Platform. The other parts of WebLogic Platform are:
a) Portal, which includes Commerce Server and Personalization Server
b) WebLogic Integration,
c) WebLogic Workshop, an IDE for Java, and d) JRockit, a JVM for Intel CPUs.
2. What is Application Server?
An application server is a software framework dedicated to the efficient execution of procedures (scripts, routines, programs …) for supporting the construction of applications. The term was created in the context of web applications. In these, the application server acts as a set of components accessible to the software developer through an API defined by the platform itself. These components are usually performed in the same machine where the web server is running, and their main job is to support the construction of dynamic pages.
3. What is the Basic Components of Weblogic Server?
These are the basic Weblogic components
Domains
Admin Server
Managed Server
Node Manager
Weblogic Server Cluster
4. What is the Domain in Weblogic server?
1) Domain is a logically related group of Oracle WebLogic Server resources that are managed as a single unit
2) Domain Provides one point of administration
3) Can logically separate:
    A) Development, test, and production applications
    B) Organizational divisions
5. What are the capabilities of WebLogic server?
Here are various capabilities associated with WebLogic server and they are
Changes in the dynamic configuration.
Production application redeployment
Rolling upgrades.
6. What are deployment descriptors?
Modules and applications have deployment descriptors—XML documents—that describe the  contents of the directory or JAR file. Deployment descriptors are text documents formatted with XML tags. The J2EE specifications define a standard, portable deployment descriptors for J2EE modules and applications.
7. What is the difference in the web.xml and weblogic.xml?
An application-specific XML-based deployment descriptor file named web.xml, which lists your application's J2EE components and their configurations as J2EE modules. Each J2EE module is a collection of one or more J2EE components of the same container type (Web or EJB) that are represented by one component deployment descriptor for that type in the web.xml file.
A WebLogic-specific deployment descriptor file named weblogic.xml, which defines how named resources in the web.xml file are mapped to WebLogic Server resources. Examples of weblogic.xml attributes include HTTP session parameters, HTTP cookie parameters, JSP parameters, resource references, security role assignments, and container attributes.
8. What is the default JVM used for Weblogic?
The sun hotspot JDK default is made used for development, JRockit is the one used for the production of WebLogic 11g as well as 12c. An operating system is another factor that helps in choosing the certified JDK JVM.
9. Is there any possibility for starting managed server during the absence of administrator server?
The usual process is that in the case of any difficulty for the manager server to get connected to any administration server at the time of start up, there is an option for the managed server to retrieve the configuration related to it from the configuration files as well as other files involved.  The information thus retrieved cannot be altered and it is possible only when the administration server is  really available. When the administration server is unavailable, then the managed server enters into its independence mode for carrying out its operations.
10. How can default JVM be changed to other?
For changing the JVM can be done by following the steps below.
You should first set the JAVA_HOME in the start script of the server.
Change the config.xml of domain for using the JRockit javac.exe
Remove any kind of switches specific to Sun JVM from start scripts of a server.
11. What are the moded of operation for Weblogic Server Domains?
Development Mode.
Production Mode.
12. Explain the term clustering?
Clustering is the process of grouping the servers together for accomplishing high percentage of
scalability and availability.
13. What is the purpose of clustering?
The major goal of performing the process of clustering is to make high scalability as well as the availability of the servers possible. This process also helps in balancing the load in a proper manner and also accomplishes failover.
14. What are the various types of WebLogic installations?
The WebLogic installation usually occurs in three different modes which are:
Graphical mode
Console mode
Silent mode.
15. What is the server?
A server is an instance of WebLogic.The server executing in a Java Virtual Machine (JVM). A server:
Runs on a designated Oracle WebLogic Server machine
Has a dedicated amount of RAM
Is multithreaded
     Two types of servers: 1) Administration Server 2) Managed Server
16. What is the Admin Server?
Admin Server is the central domain configuration interface which is used to create, delete and configure the resources of a domain like managed server, machine, cluster, data source, work managers etc.
17. What is the Managed Server?
Managed server is a server in a domain that is not the Administration server. It contacts the administration server for configuration information. It runs a business application in a production environment. It is independent of all other Managed servers in a domain (unless they are not in a cluster). You can have many managed servers in a domain. Individual managed servers are typically added for capacity and application isolation.
18. How Administration server and Managed servers will interact?
The Administration Server stores the master copy of the domain configuration, including the configuration for all Managed Servers in the domain. Each Managed Server stores a local copy of the domain configuration file. When a Managed Server starts, it connects to the Administration Server to synchronize the configuration. When the configuration is changed, the Administration Server sends the changed configuration to the Managed Servers.
19. What is the difference between Admin and Managed Server?
There is no difference between Admin and Managed server except admin interface application by default deployed on admin server which is used to configure the domain resources. Apart from that, an admin server is same as a managed server, you can deploy and create other relative resources on admin server also as you do on managed server.
20. What is the MSI mode in Weblogic? How can you enable and disable this option?
MSI is nothing but Managed Server Independence. By default, Managed Servers can function independently of the Administration Server. A Managed Server instance can start in MSI mode if the Administration Server is unavailable. Configure MSI mode from the Administration Console. To start a Managed Server in MSI mode, perform the following: Ensure that the Managed Server’s root directory contains the config subdirectory. If the Config subdirectory does not exist, copy it from the Administration Server’s root directory. Start the Managed Server at the command line or by using a script. Environment > Servers > Server_Name > Tuning > Advanced > Managed Server Independence Enabled check box.
21. Difference between Weblogic Development and Production Mode?
Here are some difference between Weblogic Development Mode and Production Mode:
Development Mode:
1) The default JDK for development domain is Sun Hotspot
2) You can use the demo certificates for SSL
3) Auto-deployment is enabled
4) Server instances rotate their log files on startup
5) Admin Server uses an automatically created boot.properties during startup
6) The default maximum capacity for JDBC Datasource is 15
7) The debugFlag which is used to start the WebLogic Workshop Debugger is enabled
Production Mode:
1) The default JDK for production domain is JRockit
2) If you use the demo certificates for SSL a warning is displayed
3) Auto-deployment is disabled
4) Server instances rotate their log files when it reaches 5MB
5) Admin Server prompts for username and password during startup
6) The default maximum capacity for JDBC Datasource is 25
7) The debugFlag which is used to start the WebLogic Workshop Debugger is disabled.
22. How to change from development mode to production mode in Weblogic 10.3?
To change Weblogic startup mode from DEV to production. One way to change it is, by simply editing setDomainEnv.cmd which resides in $root_domain/bin folder.
Look for the line that sets the PRODUCTION_MODE script variable: set PRODUCTION_MODE Add false to the value of the PRODUCTION_MODE variable to ensure the server starts in development mode: Set true for starting in prod mode. set PRODUCTI>
Save your changes and exit the text editor.
23. How to access admin console?
SSL enabled admin console accessed as https://hostname or IP address (where admin server running):(port on which admin server is
SSL enabled admin console accessed as Example - https://localhost:7001/console
Non-SSL admin console accessed as http://hostname or IP address (where admin server
running):(port on which admin server is SSL enabled admin console accessed as : Example -http://localhost:7001/console
24. What are Admin Default Ports?
The non-SSL listen port for the Administration Server’s default configuration is 7001 by default.
The SSL listen port for the Administration Server’s default network configuration is 7002 by default
Weblogic Admin servers and Managed Server’s could communicate with Admin port which is separate network channel. So that other communications can be run on different networks.
25. What is boot.proerties file in weblogic server?
boot.properties is the file used by admin or managed server during startup for username and password. it exist under your domain/servers/server_name/security folder.
26. What is config.xml?
config.xml is the central configuration repository for a domain. every resource you have configured from admin console or by command line or by any other tool registered under this file. WLS 9.x onwards, this file contain references to other XML configuration files also those are under your domain/config folder ( further subfolder under it for respective resources ) since wls 9.x onwards concept of modules are introduced for sub-resources like data source, JMS etc otherwise prior to 9.x ( 8.x or older ) every configuration was stored under this single config.xml file
27. How do I provide User credentials for starting weblogic 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 the 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.
28. What Is a WebLogic Server Cluster?
A WebLogic Server cluster consists of multiple WebLogic Server server instances running simultaneously and working together to provide increased scalability and reliability. A cluster appears to clients to be a single WebLogic Server instance. The server instances that constitute a cluster can run on the same machine, or be located on different machines. You can increase a cluster’s capacity by adding additional server instances to the cluster on an existing machine, or you
can add machines to the cluster to host the incremental server instances. Each server instance in a cluster must run the same version of WebLogic Server.
29. How to enable EJB available to servlet? assume servlet on apache, ejb on Weblogic cluster?
Any external access to EJB is not allowed. if the apache web server already configures as front-end. then we need to lookup by JNDI tree.
30. What are the reason if Managed Server is in FAILED state?
If managed server is in FAILED State there could be reason as follows:
Deployment Failed
JDBC Data Source issue
JMS Configuration issue
31. What is the advantage of clustering?
1. Scalability: The capacity of an application deployed on a WebLogic Server cluster can be increased dynamically to meet demand. You can add server instances to a cluster without interruption of service — the application continues to run without impact to clients and end users.
2. Load balancing: The ability to distribute requests across all members of the cluster, according to the workload on each server.
3. High availability: A mix of features that ensure applications and services are available even if a server or machine fails. Clients can continue to work with little or no disruption in a highly available environment. WebLogic achieves high availability using a combination of features: replication, failover, and migratable services.
32. How to monitor weblogic using WLST?
First you need to connect to the Admin Server, then you can use any Runtime MBean Using WLST we can monitor various Runtime MBean such as ThreadPool, JVM, JDBC ConnectionPool, JMS Server and Server Life Cycle for the state of a Weblogic server instance.
33. What is Mulicast and Unicast in weblogic?
Multicast: Multicast is easier to explain over Unicast. Multicast is a broadcast UDP option for sending a packet/announcement over to a group that is listening on a specific multicast address and port over which the announcement is sent.There is a defined range for valid Multicast address (224.0.0.1 to 239.255.255.255). Everyone listening on the given address hears the announcement just like following a Twitter post. Some limitations with Multicast is the TTL (time to live) across machines/subnets/routers needs to be adjusted and the routers configured to retransmit the multicast packet across subnets
Unicast: Unicast is more of a point to point UDP option to send the packet to a specific member and not everyone. That way, unicast is more of a private conversation between two individuals while multicast is more of a shout to a group or room. Both are UDP based, so there can be losses, unlike TCP that handles retransmissions on message loss. But Unicast can span across routers and does not have to worry about TTL without the everyone hearing the announcement. So, Network Admins, in general, prefer to go with Unicast over Multicast for these reasons
34. What is Horizontal and vertical clustering?
There are two methods of clustering Horizontal and Vertical.
Horizontal clustering: involves running multiple Java application servers that are run on two or more separate physical machines. Horizontal scaling is more reliable than vertical scaling since there are multiple machines involved in the cluster environment, as compared to only one machine.
Vertical clustering: however, consists of multiple Java application servers on a single physical machine. With vertical scaling, the machine's processing power, CPU usage, and JVM heap memory configurations are the main factors in deciding how many server instances should be run on one machine.
35. How Does a Cluster Relate to a Domain?
A cluster is part of a particular WebLogic Server domain.A domain is an interrelated set of WebLogic Server resources that are managed as a unit. A domain includes one or more WebLogic Server instances, which can be clustered, non-clustered, or a combination of clustered and nonclustered instances. A domain can include multiple clusters. A domain also contains the application components deployed in the domain and the resources and services required by those application  components and the server instances in the domain.
36. What is Node Manager?
Node Manager is a program that is used to control WebLogic Server instances. A single Node Manager instance is used to control all of the server instances running on the same physical machine. These instances can reside in different clusters, domains, and such. You must configure each machine in your domain to communicate with Node Manager.
37. What is the work of node manager and how do you configure it ?
Node manager is especially used for remote managed server startup. We require a logical machine created from Weblogic Admin console. Domain ---> Machines --> NewMachine --> Nodemanager (we need to provide the host and the port on which node manager is running, by default it will be localhost and 5556) Start the node manager from Beahome/weblogichome/common/bin/startNodemanager.cmd
38. How many way to start and stop weblgic servers?
There are many ways to start & stop WebLogic Admin and managed servers:
You can start and stop Admin Server using:
1) Script
2) "Java Weblogic.server "command(The Weblogic.Server class is the main class for a WebLogic
Server instance)
3) From startup option on windows
4) WLST with or without node manager
You can start managed servers using:
1) scripts 2) admin console 3) using WLST 4) using node manager 5) java Weblogic.server command( The weblogic.Server class is the main class for a WebLogic Server instance )
39. How many types you configure managed server in weblogic server?
Three types:
Domain Configuration Wizard
Administration Console
Weblogic Scripting Tool
40. 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(onWindows)
WL_HOME/server/bin/setWLSEnv.sh (on UNIX)
41. What is Machine in weblogic server?
The main purpose of a machine is to administratively manage servers.A machine required by a node manager. Machines are optionally used clusters, it is a logical description, not a physical entity.
42. How to know weblogic version?
In the WebLogic console, in the left navigation tree, click on "Environment", then "Servers". Then click on one of the servers in the list. Then click on the "Monitoring" tab. Look at the "WebLogic Version" field.
43. 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.
44. Explain the concepts and capabilities of Web Logic Server
Weblogic server supports the services and infrastructure for JEE applications. The deployment of java applications and components as services through SOAP, UDDI and WSDL, is performed by Web Logic server. The server can be configured as a web server by using its own HTTP listener that supports HTTP 1.1. The web servers of Apache, Microsoft IIS and Netscape can also be utilized. The web server configuration allows the Web Logic server to provide services to the static and dynamic requests that are generated by HTML, Servlets and JSP.
The following are some of the capabilities of Web Logic server:
Dynamic configuration changes
Production application  redeployment
Rolling upgrades
These capabilities help the availability of running systems while changes are making.
45. What is the function of T3 in WebLogic Server?
The enhancements support for WebLogic Server messages is provided by T3. These enhancements include object replacement, which work in WebLogic Server clusters’ context and HTTP. Java Object Serialization, RMI predation is done by T3. T3 is a superset of java Object. Serialization and RMI can be done over T3. Between WebLogic Servers and between programmatic clients and a WebLogic Server cluster, T3 is mandated. To communicate between processes and WebLogic Server, the protocols HTTP and IIOP can be used and optional. The HTTP is used to communicate between a browser and WebLogic Server. The IIOP is used to communicate between an Object Request Broker and WebLogic Server
46. What is difference between Connection Pool and Data Source?
1. Connection Pool is physically connected to the Database whereas Data Source is a logical resource that can be used by a developer or any other resource for resource for accessing Connection of pools.
2. DataSource can be associated with JNDI name that is used for lookup from any other client.
47. What is JMS and how do you configure it?
Java Messaging System it is an API supported by the J2EE application server for messaging between different resources.It can be used by MDB (Message Driven Beans). First you need to configure JMS System Resource, JMS module consists any one out of PTP, publisher/Subscriber type.
48. How do we Provide Load Balancing?
In Weblogic Cluster side we have 3 basic types and each supports Affinity-based also
1. Round Robin
2. Random
3. Weigh Based
49. What is the important configuration file in apache?
The Apache configuration will be defined in the httpd.conf, if required segregated Weblogic.conf file can be created. SSL enable requires httpsd.conf.
50. How to get thread dump and what is the purpose of stuck thread?
Get the java process id, you can get it by JPS or customized script for it.
Kill -3 pid for Unix Env.
Ctrl+break for windows Env.
When there is a Stuck Thread need to monitor the log for few minutes sometimes 2 or 3 stuck threads logging but after sometime it will be unstacked. If you take multiple thread dump for every 5 sec gap and analyze with samurai or Java Thread Analyzer tool you will get to know why it is stuck what is causing the instances to misbehave that time.
51. What is use of Stub?
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”.
52. How do stubs work in a WebLogic Server cluster?
The enhancements support for WebLogic Server messages is provided by T3. These enhancements include object replacement, which work in WebLogic Server clusters’ context and HTTP. Java Object Serialization, RMI predation is done by T3. T3 is a superset of java Object. Serialization and RMI can be done over T3. Between WebLogic Servers and between programmatic clients and a WebLogic Server cluster, T3 is mandated. To communicate between processes and
WebLogic Server, the protocols HTTP, and IIOP can be used and optional. The HTTP is used to communicate between a browser and WebLogic Server. The IIOP is used to communicate between an Object Request Broker and WebLogic Server.
53. In which situations server crashes ?
The server can crash because of so many reasons.
If there is any JNI code involved
If there is any native API or type2 driver involved
If there is a memory issue and then leads to an out of memory error and thereby it crashes.
54. What are the challenges in cluster environment ?
Network Architecture and multicast issues.
55. 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.
56. 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.
57. What is the difference between T3 and HTTP Protocol?
WebLogic uses the T3 protocols for internal and external connections to the servers. The T3 protocol often is used in WebLogic’s implementation of RMI Proprietary of WebLogic Server.
Http protocol is used primarily for HTTP communication between the browser and the web server.  Standard follow the W3C (World Wide Web Consortium)