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Moving to Windows Terminal Server and Thin Clients will save a company thousands of dollars each year in support costs. Multiply these cost savings by the number of PCs that can be converted to Thin Clients and pretty soon you are talking about real money. But users need to be aware that moving to a centralized server concept also means increasing dependency on a single piece of equipment, the Windows Terminal Server. Unlike other Thin Client companies, ACP recognizes the importance of delivering a system that provides a very reliable platform for the hosting of user software, and so we addressed this issue by providing true Fail-Over redundancy.
In a Thin Client system, clients can be replaced whenever needed without interrupting the application being displayed on the client, but there needs to be some mechanism for handling the demise of one of the servers. Without this protection, a server failure can mean the loss of every client connected to that server.
While there are applications that can be purchased from other companies (like Citrix) to provide for continued client operation even in the face of server failure, ACP wanted something that we could distribute as a part of our standard Thin Client management package, ThinManager. After working with a number of industrial customers, we added a server protection plan that exceeded anything available on the market. ACP's Server Fail-Over allows a user to list virtually any number of servers that can replace the primary server if it has problems. This Fail-Over is extremely fast, requires no interaction from the user and does not rely on any special server hardware.
ACP's Fail-Over is achieved through an ongoing communication between all enabled Thin Clients and their hosting Terminal Server. This continuous communication allows the client to detect a problem with its current server and use its configuration settings to determine which of the other Terminal Servers can host its session. The backup servers are usually identified when the client is put into operation, but can be changed for individual clients (or groups of clients) at anytime. And in this list of servers, the administrator can even designate a primary server, causing the client to connect to that server whenever it is available. This has the effect of causing clients that have switched to a backup server because of problems with the primary to hop back to the primary server once it comes back online.
This server Fail-Over works not only in cases where there is a problem with the server itself, but also in situations where communication with the server has failed. In fact, when we demonstrate Fail-Over to customers we don't crash the server - we simply unplug it from the hub. This results in a momentary freezing of the client's screen, followed in a matter of seconds by the client coming back to life, but this time presenting a screen generated from the backup server. (NOTE: ACP Enabled Thin Clients are the only industrial Thin Clients that also have the ability to run with two Ethernet cards, increasing network reliability for critical communication installations).
When a Terminal Server becomes unavailable, the connected clients can be configured not to reboot, but rather to search out and simply connect to the next listed Fail-Over Terminal Server. If there is a session for this client already running on the newly located server, then it reconnects to the established session. Of the few clients that offer true Fail-Over, most require a reboot of the client before it will finish the connection, and most of those also require the user to enter the IP address of the backup server. ACP realizes that very few operators are going to have that information, so we store it elsewhere on the network in settings controlled by the system administrators.
If you want the clients to switch to a backup server faster than is possible with any other Thin Client on the market, then consider ACP's Instant Failover option. A client configured with Instant Failover actually keeps two sessions (one on the primary and one on a backup server) loaded in its memory at all times. If the primary server has problems, the client simply switches to the session already established (and 'hot') for the backup server.
Every ACP Enabled Thin Client requires a running copy of ThinManager before it will boot. Therefore many users install ThinManager on the Terminal Server itself. If a system has a backup server, the clients will still have to be able to get to the licenses contained in the ThinManager package before they will boot. And if these licenses are on a server that is now down, the clients will not be able to boot from the backup server. One way around this is to install a duplicate number of ThinManager client licenses on all of the backup servers. This is clearly the best alternative, as it guarantees that any Terminal Server the client boots from will be able to supply the licenses for all of the clients. But it does get rather expensive - 20 clients will require 20 licenses on the primary server and 20 on the backup.
Another approach is to pick a third machine on the network to be the keeper of all of the ACP client licenses. The best choice for this is a machine that is required to keep the system going anyway, such as a DHCP server. The part of ThinManager that manages the license files does not put any load on the computer, so it can be added to existing equipment without putting any drain on system operation. Now whenever a client boots, whether from a primary or any of the backup servers, it will always be able to find the required ThinManager licenses.
Duplicating the server reduces the chances of catastrophic failure with only a slight increase in the administration costs, and we are finding that for most companies the security provided by a back-up server (or two) is worth the extra effort.
For more information on ACP Industrial Thin Client computers, please visit our web site at http://www.thinmanager.com
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