Component Load Balancing Shifts to AppCenter Server

After promoting Component Load Balancing as a major new feature of Windows 2000 for about a year, Microsoft Corp. has reassigned CLB from Windows 2000 to a new product called AppCenter Server.

Jim Allchin, senior vice president of the business and enterprise division at Microsoft, decided to remove CLB from Windows 2000 rather than allow customer-requested revisions to the component to further delay the release of Windows 2000, says AppCenter Server product manager Garth Fort.

Windows 2000 is expected to ship late this year or early next year. AppCenter Server has its release tentatively set for the second quarter of 2000.

The clustering feature remains available as a technology preview download on Microsoft's Web site. The download is the same version of CLB that was briefly included in the Windows 2000 beta program. The preview comes with full Microsoft support.

CLB is part of COM+, Microsoft's overhaul of its COM/DCOM application infrastructure. CLB load-balances individual components of an application across a farm of application servers, spurring faster performance and affording fault tolerance. It is one of three types of clustering among Microsoft technologies, and the only one that was new to Windows 2000. Microsoft Cluster Service for server failover and Network Load Balancing for load distribution within farms of Web servers remain in place within Windows 2000.

Testers encountered several problems with CLB between its Windows 2000 Beta 3 debut in April and its official removal with the Sept. 15 release of Beta 3 Release Candidate 2.

"We had no performance counters, no management tools, very little monitoring stuff that you could do with it," Fort says. "There was a lot of usability work that had to be done on the technology, and it will take a couple of months."

A more fundamental problem with the current iteration of CLB is its reliance on a single router to receive requests from Web servers and to balance work across the application servers. The router presents a single point of failure. Microsoft developers are working to allow each machine in a farm to act as its own router.

Fort confirms that ISVs are being told not to develop software that uses CLB because the overhaul of the feature for AppCenter Server will be major, but he denies rumors that Microsoft is considering a shift away from its COM/DCOM infrastructure to an XML-based system. "You couldn't possibly think that we are replacing RPC [Remote Procedure Call] with XML. RPC calls are still very fast," he says. XML will play an important internal role in AppCenter Server, but it won't be exposed to developers, he says.

AppCenter Server, the new home of CLB, was announced in mid-September as a building block in Microsoft's Windows Distributed interNet Architecture (Windows DNA) 2000. AppCenter is billed as a high-availability deployment and management solution for Web applications built on Windows 2000.

Running on each server in an application server cluster, AppCenter Server will provide CLB; a single application image from a central console; automatic replication of file settings and components across many servers; real-time application performance and health monitoring; self-monitoring and self-healing; and load testing and capacity analysis.

The application replication will address one of the product's most important design goals. "In Web application deployment, customers typically take an application from a set of development machines, move it to staging machines, then into production systems," Fort says. "The process of moving one of these applications is very difficult today."

Unlike client/server applications, Web applications tend to have many pieces, from executable files to Microsoft Transaction Server settings to security certificates. AppCenter Server will be designed to recognize and migrate all pieces, then keep all the application's pieces synchronized across the servers in a farm in production.

The tool will operate as a Microsoft Management Console snap-in, support remote administration via Web browser and allow for delegation of management tasks without relying on Active Directory.

Unlike Microsoft Cluster Service, developers will not need to write to a special API for their applications to take advantage of AppCenter Server and features such as CLB. Developers will have to use good Web application design principles, such as being aware of state-management, for IT administrators to wrest full benefit from the product, Fort says.

CLB was a high-level component of the Windows 2000 environment. It appeared only in Windows 2000 Advanced Server, the version of the operating system that corresponds to Windows NT Server 4.0, Enterprise Edition. Microsoft also planned to include CLB in Windows 2000 Datacenter Server, but pulled the feature from Windows 2000 before the first beta of Datacenter Server shipped in late September.

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