Web Logic Server interview questions
1. 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.
2.How are notifications made when a server is added to a cluster?
The Web Logic 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.
3.When should I use the external stage option?
Set -external stage using weblogic. Deployer if you want to stage the applicationyourself,and prefer to copy it to its target by your own means.
4.How do I provide user credentials for starting a server?
When you create a domain, the Configuration Wizard prompts you to provide the user name 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 Web Logic 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.How do you set the class path?
Web Logic Server installs the following script that you can use to set the class path that a server requires:
WL_HOMEserverbinsetWLSEnv.cmd (on Windows)
WL_HOME/server/bin/setWLSEnv.sh (on UNIX)
Where WL_HOME is the directory in which you installed Web Logic Server.
6.How do stubs work in a Web Logic Server cluster?
Clients that connect to a Web Logic 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.
7.What happens when a failure occurs and the stub cannot connect to a Web Logic 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.
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. Web Logic 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 Local Director. 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.Must Ebbs be homogeneously deployed across a cluster? Why?
Yes. In Web Logic Server 6.0 and later, Ebbs must be homogeneously deployed across a cluster for the following reasons:
To keep clustering EJBs simple
To improve performance by avoiding cross-server calls. If EJBs are not deployed on all servers, cross-server calls are more likely.
To ensure that every EJB is available locally
To ensure that all classes are loaded in an undeployable way. Every server must have access to each Ebb’s classes so that it can be bound into the local JNDI tree. If only a subset of the servers deploys the bean, the other servers will have to load the bean’s classes in their respective system class paths which makes it impossible to underplay the beans.
10.What is the function of T3 in Web Logic Server?
T3 provides a framework for Web Logic Server messages that support for enhancements. These enhancements include abbreviations and features, such as object replacement, that work in the context of Web Logic 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 Web Logic Servers and between programmatic clients and a Web Logic Server cluster. HTTP and IIOP are optional protocols that can be used to communicate between other processes and Web Logic Server. It depends on what you want to do. For example, when you want to communicate between a browser and Web Logic Server-use HTTP, or an ORB and Web Logic Server-IIOP.
11How does a server know when another server is unavailable?
Web Logic Server uses two mechanisms to determine if a given server instance is unavailable.
Each Web Logic 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
Web Logic 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.
12.How many Web Logic Servers can I have on a multi-cpu machine?
There are many possible configurations and each has its own advantages and disadvantages. BEA Web Logic 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, Web Logic Server clusters scale best when deployed with one Web Logic 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.