Time to cluster

By Dennis Brandl, BR&L Consulting -- Control Engineering, 10/1/2004

Manufacturing systems used to be based on single computers, such as PDP-11, VAX, AS-400, and Data General. These were "small-iron" systems, the little brothers of the business "big-iron" systems from IBM, Burroughs, and Univac. Today most mainstream manufacturing applications run on single Intel or AMD processors and use Microsoft Windows 2000 operating system, despite a brief flirtation with UNIX in the early 1990s.

At the same time that manufacturing applications were focusing on single-server architectures, there was a big change in business applications. Big-iron business systems were replaced with clustered servers from suppliers such as IBM, Sun, and HP. The term "clustering" is broadly defined and the hardware configuration varies based on the network used and purpose of the system, but most operate the same way. A clustered server architecture has a number of servers on the same network, all running the same applications, sharing a database, and acting as a single unified computing resource. Clustered systems form the second and third tier on three-tier systems.

The first tier is made up of the user interface of the application. The user interface makes a request for a service to a service dispatcher. The dispatcher, usually a server or network router, then routes the request to one of the servers in the cluster. If use of the application goes up or down, it is simple to add and remove servers from the cluster to match system load. Clustered server architecture provides an attractive level of scalability, and intelligent dispatchers allow upgrades by dispatching work requests to a server running the appropriate version of the application. Clustered server architectures have been used in a large number of business applications, including ERP, customer relationship management, supply chain, e-mail, and databases. However, a clustered server architecture requires that the application be designed for clustering.

While business has moved to clustering, manufacturing software vendors have not; very few manufacturing applications have been designed for clustering. Most manufacturing applications continue to follow the small-iron approach—if the system is running slow, then the user must buy a bigger and faster system. Most manufacturing applications are two-tier and inherently unclusterable. Two-tier systems, sometimes called "thick client" systems, usually have a back-end database on a server and a front-end user interface application that must be installed on each user's computer.

Newer systems follow a three-tier architecture, sometimes called "thin client" systems. Many three-tier systems use a Web browser as the first-tier user interface, an application running on a separate server as the second tier, and a database on another server as the third tier. Three-tier systems are easier to install, maintain, and extend than two-tier systems, but simply being three-tiered does not make an application clusterable. New business applications have moved beyond three-tier to "n-tier" clusterable applications. In n-tier applications, one application may use services from many other applications and user interfaces may merge elements from multiple applications. In a new business system, the number of applications supporting a single user view may be immense, with data sources and data sinks on widely divergent systems.

Because it seems to take about five years for mainstream business technology to be applied in manufacturing, we should start to see clustered server architectures and n-tier manufacturing applications within the next couple of years—but these applications are needed now. Without a clustered system architecture there must be one large single system for the entire plant or physical partitioning, such as one SCADA or MES system per process cell or production line. Neither solution provides the extensibility and upgradeability needed in modern manufacturing plants.

Dennis Brandl, dbrandl@brlconsulting.com, is the president of BR&L Consulting, a firm focusing on manufacturing IT solutions, based in Cary, NC.