This Knowledgebase article provides general guidelines for the use of local management or client tools for protected applications.
In some cases, such tools may lock files on the passive server, leading to a possible 'out of sync' condition for the protected file system. This has implications for Neverfail Heartbeat's switchover operation.
Additionally, some files used by the management client may appear in the protected set. In some other case, like Good Mobile Messaging and IIS, use of the protected application management client can actually result in services starting on the server. This is undesirable as it will result in apply exceptions occurring on the application data.
Many server applications use management client tools, which can be run remotely, from a client machine, or locally on the server hosting the application.
Remote management client tools generally have no impact on the operation of Neverfail Heartbeat, since they do not open or lock files on the server. Local client tools, on the other hand, may open or lock such files. In normal operation, this is not an issue - the client will be run on the active server in the pair (since the protected application is shut down on the passive server), and will not interfere with Neverfail's file replication and synchronization processes, even if those files which are in use are part of the protected file system.
On the passive server, the impact of such a client tool is more serious. Neverfail Heartbeat may not be able to synchronize a file, which is held open by a client tool on the passive server.
The most likely sequence of events leading to this condition is as follows:
- A management or client tool is opened locally on the active server, and left open.
- A switchover occurs, triggered either manually, or by a Neverfail Application Module.
The active server will become passive while the management or client tool is still open, and still interacting with the protected file system. If this does happen, the management service should be stopped after the management client is closed on the passive server.
In order to avoid this situation, you should always close any local application management clients on the active server when they are not in use, or prior to performing a switchover.
Note: This advice does not apply to the Neverfail Heartbeat Management Client, which may be run on the active or passive server at any time, provided Neverfail Heartbeat is also running.
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