WebSphere Application Server Node Agents

Node Agents in WebSphere Application Server 

A Websphere Node is a logical grouping of server processes managed by WebSphere and that share common configuration and operation control. A node is a grouping of managed or unmanaged servers. A node usually corresponds to a logical or physical computer system with a distinct IP host address. Nodes cannot span multiple computers. Node names usually are identical to the host name for the computer.

Nodes in the network deployment topology can be managed or unmanaged. A managed node has a node agent process that manages its configuration and servers. Unmanaged nodes do not have a node agent.

A node corresponds to a physical computer system with a distinct IP host address. The node name is usually the same as the host name for the computer. The following table lists the nodes in this cell. You can add new nodes into the cell by clicking on "Add Node" and specifying a remote, running WebSphere Application Server instance.

The Websphere Node Agent represents the node in the management cell and keeps the configuration up to date. Node agents are administrative agents that represent a node to your system and manage the servers on that node. Node agents monitor application servers on a host system and route administrative requests to servers.

A Websphere Node Group is a new concept introduced with WebSphere Application Server V6. A node group is a grouping of nodes within a cell that have similar capabilities. A node group is a collection of managed nodes.

Read more...

WebLogic Server Load Balancing

Load Balancing in WebLogic Server 

Load balancing is about distributing work across multiple servers within a cluster. Ideally you want this work to be distributed evenly, to the capabilities and load on each server within the cluster. WebLogic is able to load-balance requests to members within a cluster when certain conditions are satisfied.

First, WebLogic requires that (most) components be deployed homogeneously to each server in the cluster. In the multi-tier application setup, the web application is targeted to all servers that belong to the presentation tier cluster. Because of this, incoming requests can be distributed evenly across the different members of the presentation tier. Similarly, the EJB components are available on all members of the object tier cluster. Because of this, incoming EJB calls from the presentation tier (or any external client) can be distributed across the different servers in the object tier.

When a component is deployed to a cluster, multiple copies of the component will be sitting on the different servers comprising the cluster. WebLogic uses the cluster-wide JNDI tree to record the availability of these replicas in the object tier, whereas a proxy plug-in typically holds the information about the availability of servers hosting the servlets and JSP pages.

WebLogic also must be aware of the status of the components that have been deployed to the cluster. This information forms the basis on which a load balancer can decide which server instances should be used when a request is made to the cluster. WebLogic uses a variety of methods to determine the health status of servers, including multicast heartbeats. By knowing when a server instance is under heavy load while the others aren't, a load balancer is able to direct new requests to the other members of the cluster. Hardware load balancers often have this capability

Read more...

Accessing the Java Spring Container

How to access the java Spring Container:

Java Spring is an open source, lightweight, application framework that is intended to help structure entire applications in a consistent manner, pulling together best of breed single-tier frameworks in
a coherent architecture.

From Stand-alone:

ApplicationContext context = new
ClassPathXmlApplicationContext(APP_CONTEXT_CLASSPATH);
(APP_CONTEXT_CLASSPATH is spring/pam-contact-loader-spring-context.xml)

From Web Application

ApplicationContext context =
WebApplicationContextUtils.getWebApplicationContext(
pRequest.getSession().getServletContext());

web.xml modification

<ltcontext-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/classes/spring/pam-spring-context.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listenerclass>
</listener>

Read more...

WebLogic Clustering

Clustering  in WebLogic

A WebLogic domain can be composed of a number of WebLogic instances, and several of these servers may be grouped into clusters. The Domain is the parent of a Cluster. It contains typically one Admin and one or more Managed servers. Now the Cluster is a grouping of some or all of these managed servers within the domain.For instance, you could set up a cluster of WebLogic servers, all of which host your web application and related resources. This cluster of servers could be fronted by a load balancer that distributes requests evenly across all the members of the cluster. The load balancer could itself be another WebLogic instance. All server instances must belong to the same WebLogic domain. 

Thus, a WebLogic cluster is a group of servers working together with services, such as clustered JNDI, to provide support for failover and load balancing. A domain may in turn have a number of WebLogic instances, several groups of which can be placed into different clusters.

Read more...

Difference between Web Server and Application Server

Webserver A Web server handles the HTTP protocol. When the Web server receives an HTTP request, it responds with an HTTP response, such as sending back an HTML page. To process a request, a Web server may respond with a static HTML page or image, send a redirect, or delegate the dynamic response generation to some other program such as CGI scripts, JSPs (JavaServer Pages), servlets, ASPs (Active Server Pages), server-side JavaScripts, or some other server-side technology. Whatever their purpose, such server-side programs generate a response, most often in HTML, for viewing in a Web browser.

Web servers are technology designed to create and deploy Web site, serving up content more so than applications. They both use Web interfaces, but Web servers are more about the interface than the back-end logic. In other words, Web servers serve up content. As time moves on Web servers are looking more like application server, as they adopt their functionality.  

Application Server As for the application server, according to our definition, an application server exposes business logic to client applications through various protocols, possibly including HTTP. While a Web server mainly deals with sending HTML for display in a Web browser, an application server provides access to business logic for use by client application programs. The application program can use this logic just as it would call a method on an object.

An application server is technology where developers can create, test, and execute application components. Application servers are typically J2EE-based, running EJBs or other Java components. Application servers are designed to create true applications with complex business logic, and have scalability features such as load balancing, fail-over, and process distribution. In other words, it's primarily a development environment.

Read more...

Difference between JRE/JVM/JDK

JDK is the Java Development Kit i.e. JDK is bundle of software that you can use to develop Java based software. JRE is the Java Runtime Environment i.e. JRE is an implementation of the Java Virtual Machine which actually executes Java programs. Typically, each JDK contains one (or more) JRE’s along with the various development tools like the Java source compilers, bundling and deployment tools, debuggers,development libraries, etc.

Read more...