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There are really what could be considered two servers involved with every ThinManager Ready Thin Client. The most obvious one is the Windows Terminal Server that will host the client. This is the server that will actually run the application displayed on the client's screen. The second 'server' involved is the ThinManager License server. Understanding the difference in these two machines is vital to understanding Thin Client redundancy.
When any ThinManager Ready Thin Client boots, one of the first things it does is locate a valid license from the ThinManager license server. Once it receives this license, it is directed to the correct Windows Terminal Server to start the session. For the Thin Client to run correctly, both of these machines must be running. If the Thin Client attempts to boot and does not find this valid ThinManager license, it stops during the boot process. If it boots and finds a valid license from the ThinManager License Server but the Windows Terminal Server is not running, it cannot log in and start a session. |
Thin Clients with ThinManager License Server and Windows Terminal Server |
For many installations, the ThinManager licenses are actually installed on the same Windows Terminal Server that is hosting the Thin Clients. This makes the ThinManager License Server and the Terminal Server the same physical machine. This has the advantage of ensuring that all Thin Clients connecting to Terminal Servers have a valid license. As long as the Terminal Server is running, the Thin Client can boot, receive a valid license, and then log in and start a session.
For larger installations, the ThinManager license server is usually a different machine on the network. This is especially true for ACP's Enterprise licenses. Each Thin Client on the network boots, receives a valid license from the License Server and is directed to one (or more) Windows Terminal Servers on the network to log in and start its session(s).
Thin Client installation with primary and backup Terminal Server |
When ACP talks about redundancy, there are really two machines that can be made redundant. There could be a primary and backup Windows Terminal Server, and a primary and backup ThinManager License Server. This can be achieved by installing the ThinManager Licenses on each of the primary and backup Terminal Servers. It can also be achieved by having two ThinManager License servers on the network. As the load on the ThinManager License server is extremely light, these do not have to be large machines. Also, each ThinManager License server can validate the licenses for thousands of Thin Clients. |
When ACP speaks of Failover, we are almost always talking about allowing the Thin Client to swap to a backup Windows Terminal Server if the primary server has problems. This is how many of our customers configure their systems, and is almost required for industrial installations. Remember that the ThinManager license server is only needed when the Thin Client boots, so once booted it can switch among any number of Terminal Servers without ever needing to recheck the license.
The ideal installation will have backups for both the ThinManager Server and the Windows Terminal Server, as shown below.
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Thin Client installation with primary and backup Windows Terminal Server and primary and backup ACP ThinManager server |
Also, ACP only licenses the actual Thin Clients, not the number of connections to the Terminal Servers. So from a single 5 license pack a user could boot 5 Thin Clients and each Thin Client could connect to 10 (or more) Terminal Servers, running a huge number of total sessions at the same time.
While any ThinManager Ready Thin Client can be configured to automatically fail to a backup Terminal Server if the primary Terminal Server becomes unusable, this can take a little time because it has to locate the backup server, log in and start the application. ACP's Instant Failover is an additional module that allows a single Thin Client to simultaneously log into two different Terminal Servers (a primary and a backup) and have the second session always ready to go. Not only can the user switch between the two sessions with a hot-key sequence, but if the primary server fails the Thin Client will instantly display the screen from the backup server. Without Instant Failover it could take 10 to 15 seconds to log in and display the other session.
For a much more detailed treatment of the issue of failover and redundancy, please visit the ACP technical article referenced below:
For more information on ACP Industrial Thin Client computers, please visit our web site at http://www.thinmanager.com
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