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Using Monitored Server Scripts

Using Monitored Server Scripts

FusionReactor Enterprise Scripting enhances FusionReactor's Enterprise Monitoring to trigger configurable self-healing scripts when a server's responsiveness status changes.

This feature can be used to perform any task which can be launched from a platform script.

Examples might include:

  • Interacting with SNMP or enterprise monitoring/reporting systems
  • Performing automated restarts of affected instances
  • Sending custom email messages
  • Writing custom log messages

Since FusionReactor Enterprise Scripting is able to launch any platform executable (shell script,executable binary etc.), it may be tailored to virtually any environment.  

Note

To use this functionality AT LEAST two different instances of FusionReactor Enterprise are REQUIRED.  It is important to understand this limitation of scripting. A script should not be configured to run against the same server instance that FusionReactor is running in. If the server instance fails then the FusionReactor running in this server instance may not be able to run the script, meaning it may not be able to restart itself for example.

What Are Enterprise Scripts?

FusionReactor (Enterprise Edition) can trigger a script when a server becomes unresponsive, and when it becomes responsive again. This mechanism might allow you to pro-actively attempt to restart a failed server or instance, integrate FusionReactor into an existing monitoring environment or provide custom logging or reporting. Any program which is runnable on your FusionReactor monitoring system may be used by an Enterprise Script target.

Enterprise scripts on Windows systems, are anything that is runnable as a binary, or can be run from the command prompt, for instance:

  • Binary programs
  • Batch files

Enterprise scripts on Unix and Unix-based systems, this includes everything you can start from a command line, for instance:

  • Binary programs
  • Shell scripts (including Bash, Ruby, Python and Perl)
  • Java programs (when launched from an appropriate shell script)

How Do I Configure an Enterprise Script?

Enterprise scripts are configured by editing the Script of the server's property page, accessible in the Enterprise -> Manage Servers page, then clicking on the Modify icon of the required server. You should take care to ensure the full path and filename to the script are correct. Also note that it is recommended to only configure one script for a server. If the same server has multiple scripts configured (for example you have entered the server into the dashboard in multiple groups) or you monitor the same server from different machines, then more than one script may be launched at the same time if the server has problems. The scripts may interfere with each other especially if they are trying to restart the same instance.

When Does FusionReactor Run Enterprise Scripts?

Enterprise Scripts are run whenever the Enterprise Monitor detects that a monitored instance has changed state:

  • an instance which was previously available is no longer providing Enterprise data
  • an instance which was previously unavailable has begun to provide Enterprise data

Scripts are run only if an instance changes state while it is being observed. Additionally, scripts are only run if:

  • The Enterprise Server Alerting system is running
    • This is configured in Enterprise Settings -> Server Shutdown/Start Up Alerts
  • At least "On Shutdown" must be selected.
    • If you wish to run scripts when an instance becomes available, "On Shutdown and Start Up" must be selected.
    • If you do not wish to additionally receive email for these events, disable notification in FusionReactor -> Settings -> Email Server -> Notification.

How Does FusionReactor Run These Scripts?

Launch Mechanism

FusionReactor runs these scripts by spawning them using Java system commands. The scripts will be run in the context of the user under which your J2EE (ColdFusion) server runs. This user must have at least read + execute access to these scripts. Any files or other executables called by the script must also be accessible by this user.

The script will be run with the current working directory (CWD) of the J2EE application server. Because of the variety of platforms available, this may be unpredictable. Any scripts you write should therefore not use the current directory notation (usually a single dot) to address files. If you plan to access files within the script, their paths should be specified completely.

Script Arguments

FusionReactor supplies several command-line arguments to the script. These arguments may be used by the script to perform logging or restart operations. Note that these arguments are supplied by FusionReactor and you do not need to enter them in the script field on the Managed Servers page. The supplied arguments are (in order):

Script Parameter Description
UP or DOWN reflecting the instance status
Instance Name as registered in the Manage Servers screen
IP Address as returned from a DNS lookup of the machine name part of the URL used to monitor this instance
Process ID If available, the process ID of the J2EE application server on the remote machine. If the FusionReactor native library is not available, or FusionReactor could not read this value, this field will be -1
Last Seen Time The time, measured in milliseconds from midnight on January 1st 1970, which the server was last successfully polled for Enterprise data. If the server has not been observed as running during this session, this field will be -1

Logging

When FusionReactor fires a script, an appropriate message is written to the Crash Protection log, located in FusionReactor/instance/<instance_name>/log/crashproteciton-0.log. This log is shared with other Crash Protection messages, and not all fields are used by Enterprise scripting.

For the exceptional cases SCRIPTREADFAILED and SCRIPTEXCEPTION, FusionReactor will log the message associated with the exception to the FusionReactor log.

Operational Impacts of Scripting

There are a few points which you should bear in mind when configuring scripting.

System Restarts and Self-Monitoring

If FusionReactor is configured to monitor itself, i.e. it is monitoring the same instance in which it is configured, scripting should not be used for operations.

In these circumstances, we recommend transitioning your environment to a High Availability monitoring solution. This entails installing a new J2EE server (Tomcat, for instance), and installing FusionReactor into that. This container will be used purely as a FusionReactor host, and will be used to monitor other containers. It may be necessary to create scripts which perform system reboots. Again, we recommend a careful evaluation of the impacts of this type of script before implementation. A script which restarts a system should not attempt to restart the system on which the monitoring solution runs.

Manual Restarts

If a script is configured for a given instance, it will be fired when that instance becomes unavailable. FusionReactor does not differentiate between overloaded (or failing) instances, and instances which have been deliberately stopped. Therefore, if you stop an instance manually, through Windows' Services panel for instance, FusionReactor will fire the configured script. As an operational matter, the affected instances should be "offlined" from FusionReactor before being shut down. This can be done within the Enterprise Dashboard, by clicking the (+/-) button on the top right of server icon or from within Manage Servers by selecting the Modify icon for the affected server, then changing its Status to Offline. FusionReactor will not monitor these systems. When maintenance is complete, the servers should be "onlined" again by reversing the process.

Using the Example Scripts

We have provided several restart scripts to get you started. This section will help you understand how to install and configure them.

Installation

The example scripts are provided in /FusionReactor/etc/cp/, thereafter the structure is split into scripts which will run on Unix platforms, and those which will run on Windows platforms. You are free to run these scripts from this location, but we would recommend you copy these templates before editing them. You will then always have a pristine copy available for new scripts.

Worked Example: Controlling Windows ColdFusion 8 from Windows

In order to get you started, we've provided you with a worked example. In our example scenario, we will use a FusionReactor Enterprise Edition instance on a ColdFusion 7 instance to monitor a ColdFusion 8 installation, also on Windows and running FusionReactor Enterprise Edition.

Enterprise Dashboard

The first stage in preparing the environments is to ensure that both systems are running smoothly, and the monitor is able to poll the target system for enterprise data. Add the remote system to the monitor and check that Enterprise Dashboard is retrieving information from it.

Script Preparation

For this example, we'll be using the restart-Coldfusion8-OnWindows.bat script from the FusionReactor/etc/cp/windows folder. For our example, we copy the example script to a temporary folder, from where we can work on it:

copy restart-Coldfusion8-OnWindows.bat c:\tmp

In order to customize the script, we open it in an editor. All provided example scripts are commented extensively.

There are a couple of variables we must customize in the script:

  • We set the LOGFILE (line 43) to c:\tmp\script.log
  • We change the USER and PWD (lines 53 and 54 respectively) to reflect the Windows user with permissions to restart ColdFusion.
Adding the Script to Manage Servers

The final step in the configuration is to add the script to the monitored server's configuration. We edit the server's Enterprise Dashboard configuration by clicking on Manage Servers, then clicking the edit icon of the monitored server. We enter the script location in the Script field.

Testing the Script

The script can be tested by simply using the Windows Service control panel to stop the monitored ColdFusion 8 service. Observing the script log file c:\tmp\script.log file shows the output of the script. The ColdFusion 8 service can be observed restarting in the control panel.

Conclusion

We've shown you how to configure Enterprise Scripting to restart a ColdFusion 8 server. The scope for what scripts can do is immense, since there are no restrictions on what they may call. It would be a simple task, for example, to integrate FusionReactor into an SNMP monitoring solution, write custom log messages or send SMS text messages.

Local Monitoring: Monitoring Instances on the same computer as the Enterprise Monitor

Running all FusionReactor instances on the same computer makes it easy to develop scripts for use with Crash Protection.

Simple Watchdog

Two instances run on the same computer. One of the instances acts as an Enterprise Monitor (Watchdog) for the other, monitored server. The watchdog server has added the monitored server to the list of managed servers in the Enterprise Dashboard of FusionReactor. A script for the monitored server is configured that will be executed by the watchdog server if the monitored server is unavailable or becomes available again. The script is used to restart the monitored server automatically after it became unavailable.

However, if the watchdog server itself becomes unavailable, the server is not longer monitored and can not be restarted automatically any more. To get around this the monitored server could also monitor the watchdog server which is described in the next section.

Cross Monitoring

One instance/server is created for the task of Enterprise Monitor to monitor the other Operational servers. Every operational server is added to the Enterprise Monitor's list of managed servers in the Enterprise Dashboard of FusionReactor. For every server a script is configured that will be executed when the server becomes unavailable (or available again). The script is used to restart the operational server automatically if it becomes unavailable. One of the operational servers is also configured to monitor the Enterprise Monitor, and a script is configured to restart the Enterprise Monitor should it become unavailable. If this way the Enterprise Monitor watches over all of the operational servers, and one of the operational Servers watches other the Enterprise Monitor. Alternatively a second Enterprise monitor could be configured with the task of watching over the first Enterprise monitor if you do not want operational servers to perform monitoring tasks.

Distributed Monitoring

Running, monitoring and restarting FusionReactor instances in a distributed environment requires remote connections between the different machines. If a monitored server becomes unavailable this is monitored by a different machine on the network. This machine then calls a script which has to connect to the remote machine and restart the remote server/instance. Depending on the operating system the participating machines use, this can be done with (SSH) or some similar technology.

Simple Watchdog

Two servers run on different machines that have a network connection. One of the servers acts as the Enterprise Monitor (watchdog) for the other, monitored server. The watchdog server has the monitored server entered in it's list of managed servers in the Enterprise Dashboard of FusionReactor. A script for the monitored server is configured that will be executed by the watchdog server if the monitored server becomes unavailable (or available again). The script is used to login to the remote computer and restart the server/instance automatically after it becomes unavailable. This approach can have the same drawbacks as mentioned in the Local Server Simple Watchdog section before.

Cross Monitoring

All servers run on different machines that can reach each other over the network. One instance/server is created for the task of Enterprise Monitor to monitor the other Operational servers. Every operational server is added to the Enterprise Monitor's list of managed servers in the Enterprise Dashboard of FusionReactor. For every server a script is configured that will be executed when the server becomes unavailable (or available again). The script is used to login to the remote computer and restart the operational server automatically if it becomes unavailable. One of the operational servers is also configured to monitor the Enterprise Monitor, and a script is configured to login to the Enterprise Monitor computer and restart the Enterprise Monitor instance should it become unavailable. If this way the Enterprise Monitor watches over all of the operational servers, and one of the operational Servers watches other the Enterprise Monitor. Alternatively a second Enterprise monitor could be configured with the task of watching over the first Enterprise monitor if you do not want operational servers to perform monitoring tasks.

Summary

FusionReactor Crash Protection Scripts are powerful functionality that can lead to an increase of server availability in local as well as distributed server environments.

Warning

You must however be aware of that a script that is executed by a Crash Protection rule is executed by the server instance that is monitoring the problem server and not by the problem server itself. If this is not the same computer, remote scripting has to be used to react to the situation in an appropriate way. Also note, that you should not use scripting in a single instance (self-monitoring) scenario, because the script may not reliably start.