3.2.2 Monitoring a server in monitor mode (for the standby server)
This subsection describes a function that enables monitoring in the standby system in the monitor mode. With this function, you can start processes, and can monitor processes and resources, in the standby system. For example, this function can be used in the following cases:
- When creating a hot-standby switchover configuration in which the processes of an application run on both the active system and standby system
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A feature of the function that enables monitoring in the standby system in the monitor mode is that the user can start and monitor applications even in the standby system. For example, this function can be applied to an application whose processes run in both the active system and standby system to synchronize their data.
The following figure shows a hot-standby switchover configuration that uses an application whose processes run in both the active system and standby system.
Figure 3‒3: Hot-standby switchover configuration that uses an application whose processes run in both the active system and standby system ![[Figure]](GRAPHICS/F0000045.GIF)
- When detecting an error by monitoring processes and resources (such as LAN and disk paths) in the standby system
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The function that enables monitoring in the standby system in the monitor mode can be used to monitor processes and resources (such as LAN and disk paths) in the standby system. If a failure is detected in the standby system, you can select either of the following types of system behavior:
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HA Monitor stops the standby server so that hot-standby switchover cannot be performed.
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HA Monitor attempts to restart the standby server so that hot-standby switchover can be performed. After the standby server is restarted successfully, if the monitoring command does not return a failure for a certain period of time, HA Monitor assumes that the standby server is running stably, and resets the number of start retries.
The preceding behavior can prevent task operation from discontinuing if hot-standby switchover occurs before the standby system is recovered from a failure.
The following figure shows an example of monitoring a resource (path to the shared disk) in the standby system.
Figure 3‒4: Example of monitoring a resource (path to the shared disk) in the standby system ![[Figure]](GRAPHICS/F0000046.GIF)
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- Organization of this subsection
(1) Method of monitoring
During monitoring in the standby system in the monitor mode, any commands can be executed to start, stop, and monitor the standby server#. The standby server is stopped or restarted according to the command execution result.
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In a multi-standby configuration, all standby servers are subject to the command regardless of priority. In this case, the standby server monitoring command is executed on all standby servers. Therefore, make sure that the active server is not affected when, for example, resources are being monitored.
The monchange command allows you to change the settings and operations while HA Monitor and servers are running. You can use this command to temporarily stop and restart server monitoring. For details, see 9.6 monchange (changes settings and operations while HA Monitor and servers are running).
(2) Required environment settings
To perform monitoring in the standby system in the monitor mode, use the following procedure to specify the environment settings:
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Create commands that will be used to start, stop, and monitor the standby server.
For details about how to create the commands, see 6.14 Creating commands that will be used to start, stop, and monitor the standby server (in the case where monitoring is performed in the standby system).
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Specify the commands created in step 1 for the following operands:
- Server environment definition: