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ACP Thin Client Newsletter Article |
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We have two terms we use that are easily confused but actually mean different things - Failover & Redundancy. Briefly, Failover occurs when a Thin Client can no longer communicate with the Terminal Server that is hosting its application. Without contact with the Server the Thin Client has nothing to display. Thin Clients running under ThinManager have always been able to detect this situation and go in search of a backup Terminal Server. These servers are configured for each client by listing all of the available Terminal Servers in the client's configuration. If the current server becomes unavailable the client tries the next server, and so on, until it finds one that will let it run a session.
Redundancy provides backup for the ThinManager license itself. When each Thin Client boots it searches for a valid ThinManager connection license (a 5-pack, 10-pack, Enterprise license, etc.). Once it finds this license it looks at the Terminal Servers in its list and makes a connection. It does not check this ThinManager license again until it is rebooted.
The ThinManager licenses are frequently kept on the Terminal Server itself, but they do not need to be. Many customers decide to deploy 5 Thin Clients and purchase a Terminal Server, install ThinManager on the server, add a ThinManager 5-pack to it and start running their applications. If they are worried about what happens if the single server goes down (and they lose displays on all 5 clients) they will add a second Terminal Server and configure it for Failover.
If they want to make sure that the clients can reboot when the primary server is down they may also purchase another 5-pack for the backup server. This provides Redundancy of the ThinManager licenses. While they technically now have 10 licenses, they only run 5 clients and use the second (Redundant) 5-pack for backup only.
This is easier to understand with larger systems. The customer who is deploying 1,000 Thin Clients and using 50 Terminal Servers will not try and install 20 ThinManager licenses on each Terminal Server - instead he will install all 1,000 licenses (or an unlimited Enterprise license) on a single machine that he will use as a ThinManager license server (we call it a ThinServer). Each client will hit that license machine as it boots and then trot off and connect to the appropriate Terminal Server. In this case Redundancy is very important, because if that single license server is out of commission then none of the clients can boot. That is why our Enterprise Server licenses can be installed on two machines - a primary and a backup.
A Mirrored License on the other hand has nothing to do with failover. Instead it provides a license that ThinManager will put on a primary and a redundant ThinServer. It differs from the case where the customer purchases twice as many licenses as he has Thin Clients because the Redundant ThinServer cannot host the ThinManager user interface. The customer will still be able to reboot his clients from the backup machine, but until the primary machine is available he will not be able to shadow the clients, check status of clients and servers, reboot any clients or change any configuration. With Mirrored Licensing the second ThinServer has less flexibility but it provides for license Redundancy at a lower cost.
For more information on ACP and Thin Client management software, please visit our web site at http://www.thinmanager.com
For an archive of past newsletter articles, or to sign up for this monthly newsletter online, please visit our newsletter index at Past Articles
(c) Copyright 2007 Automation Control Products. All rights reserved. All product names contained herein are the trademarks of their respective holders.
