Friday, November 7, 2014

Let Operations Drive Server Architecture

Posted by John Harrington

Many people ask, "What is the optimal architecture for KEPServerEX within a plant; how many servers and where?" As with most questions of this nature, the short answer is that it depends, but there is some guidance we can provide.

With other software applications, architectural decisions Lightbulb_Gearstypically would be made based on weighing software scalability with software cost; however, Kepware has designed KEPServerEX such that it is able to scale up for large implementations while retaining a small footprint for small implementations. Kepware has some customers with over 1 million tags in the server, and other customers with only 10 tags in the server. Kepware has priced KEPServerEX such that additional servers will not significantly increase the cost of a project: a server with single driver is less than $1,000 and a server with the Manufacturing Suite (with over 100 drivers) is less than $2,500. By taking cost and scalability considerations off the table, Kepware is striving to allow customers to make their architectural decisions based on Operations and how they run their plant and IT systems.

When defining the best practice architecture, Operations should look at the layout of the physical plant, the requirements of the client software, and the network architecture and security needs of the IT systems.

Plant Floor Layout

As with any software, there will be times when you have to restart the server or stop all operations to implement certain changes like installing new versions of the software, adding additional licenses to the server, or performing server hardware or operating system updates. The effects of this can be minimized, but ultimately periodic downtime should be expected. Many factories or operations have multiple logical sections within the factory. The material flow within each section is continuous and the machinery is tightly integrated; however, the material flow between sections is not continuous and the machinery is not tightly integrated. In a small discrete manufacturing plant, there may be sections for machining, assembly, painting, inspection, and packaging. With such a layout, it would also make sense to have five server installs—one for each section or zone. In other cases, a single work cell may require its own server. This would be if the cell primarily operates autonomously, if the equipment changes frequently (which would require many changes to the server), or if the hardware and software for the server are updated frequently.

Client Requirements

Another approach is to evaluate the necessity of information to client software. There are many different types of software clients that connect KEPServerEX for plant floor information, from HMI and SCADA to MES and ERP to custom analytics, web, or mobile applications. Some clients are mission-critical, and if they lose their connection to the plant floor, the floor must come to a stop (such as because they are controlling the floor with a SCADA or MES program or because they are historizing information from the floor for regulatory purposes). In either case, they may require a dedicated server or even a redundant pair. Other clients may be used for monitoring operations, production or quality analysis, or mobile access. These are important systems, but the factory does not come to a halt if they are interrupted for a short period of time. A typical implementation is to have multiple of these non-critical clients on a single server: this minimizes both the load on the PLC (by not having many servers opening connections) and the system administration (by reducing the servers).

Network Architecture

The final consideration is to evaluate the network architecture and cyber security requirements. In many companies, the Operations applications are separated from the business IT applications by a firewall. In this case, putting a server in the IT network and using a secure tunnel to one or multiple servers on the Operations’ side provides multiple levels of cyber security. The IT server can be shut down if it is violated, and the operational servers can restrict the information and level of access available to the IT server.

Conclusion

There is not a one-size-fits-all approach to server architecture for a factory or automation operation—there are only guidelines that can be recommended and key information that should be evaluated. In the end, letting the operations of the plant drive the quantity and organization is much better than cost, software scalability limitations, or ignorance.

Best Practice Considerations

Plant Floor

  • Natural process separations
  • Areas being changed or upgraded frequently

Client Requirements

  • Critical applications vs. secondary applications

Network Architecture

  • Firewall Access
  • Cyber security

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