Introducing Application Center
For customers who are building and managing Web applications, three key issues must be addressed:
Manageability. How easy is it to update and upgrade the Web site content?
Scalability. How does the Web site cope with additional demand?
Availability. Will the Web site be available 99.99 percent of the time?
Microsoft Application Center 2000 (Application Center) is the management and deployment tool that solves these issues for Web and COM+ applications.
The fundamental basic of Application Center is the cluster. This is a set of servers that serve the same content to cluster users.
An Application Center cluster can serve internal corporate intranet clients or external Internet clients. The client software can be "thin-client" (such as Web browsers) or "thick-client" applications (such as Microsoft® Visual Basic® programs). Application Center clusters are designed to manage both the Web tier, which serves HTTP clients and the business logic tier, which serves DCOM traffic.
Using Application Center clusters, Web site administrators can address the issues of manageability, scalability, and availability.
Note Application Center clusters are not the same as clusters as defined by Microsoft Windows® Clustering. The Windows Clustering model was designed to handle stateful back-end applications, such as Microsoft SQL Server™ databases or Microsoft Exchange Server stores; Windows Clustering uses a shared disk resource to coordinate between cluster members. Application Center clusters are designed for stateless, middle-tier applications, such as Web sites and COM+ applications, and they do not require a shared disk (or any special hardware).
Note You can use Application Center to manage availability and application deployment on stand-alone (non-clustered) servers or servers that are not running Web sites. In these cases, Application Center treats the stand-alone server as a "cluster of one."
The Application Center snap-in provides a single, unified image of the content that is installed across a cluster. Application Center provides wizards that simplify the process of creating and managing clusters and deploying content. Furthermore, Application Center supports remote, browser-based administration and provides a command-line tool.
In Application Center, the concept of an application is used to define the content that a cluster serves to its clients. An Application Center application includes all the necessary elements (that is, Web sites, COM+ components, configuration settings, and so on) for a given business solution. The application is used as the unit of content deployment across a cluster. Once you have defined an application, Application Center can keep the contents for the application synchronized across a cluster, or it can deploy a new version of the application within a cluster and to other clusters.
Client demand on Web sites changes frequently. Application Center can easily accommodate changing throughput needs because it simplifies the process for adding members to or removing members from a cluster. This is done with no interruption to Web site availability. Furthermore, Application Center uses load balancing to distribute workload throughout a cluster. Application Center is compatible with the leading hardware load-balancing devices. Application Center includes two software load-balancing technologies: Network Load Balancing (NLB) and Component Load Balancing (CLB). NLB is used to balance IP requests across a cluster and CLB is used to balance the activation of DCOM requests. Appllication Center is also compatible with other load-balancing devices.
To provide high availability, Application Center clusters have no single point of failure. If one member fails, clients can continue to access the application through other members. The monitoring tools that are provided with Application Center detect hardware and software failures automatically, and can trigger actions, such as running scripts or sending e-mail notification, in response to a failure. Additionally, Application Center monitoring is tightly integrated with NLB, so that you can easily configure a member to go offline when an application level failure occurs.
To help you pro-actively improve system performance and availability, Application Center rolls up event and performance logs across a cluster, enabling a cluster-wide view of performance trends and simplifying event management.
For more information about the hardware and software requirements for clusters, see Installation Requirements.
For more information about setting up cluster communication, see Configure Cluster Communication.
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