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Configuring Clusters


Using JRun probes

ClusterCATS provides load-balancing and failover support for your web applications in two ways. First, it automatically interprets and reacts to the load metric that the JRun servers generate. Second, ClusterCATS lets you create web application monitors. These monitors can have multiple probes that periodically test the health and operation of the websites that the JRun servers process.

Note:   Multiple JRun probes are allowed per web server, and JRun web applications can be restarted individually. However, each web application should have only one probe that restarts on a failure.

The probe is a high-availability feature that verifies that JRun servers are running properly on clustered servers. It periodically tests specific JRun URLs at specified intervals and verifies their validity against user-defined strings contained in the returned pages.

If the validation test succeeds, inbound HTTP requests continue to be sent to the server for which the probe exists. However, if a test fails (the URL fails, times out, or does not return the user-specified string in the page accessed), ClusterCATS restricts that server and redirects requests to other available servers in the cluster. ClusterCATS continues to test the restricted server; when he probe returns a valid value, the server is considered available.

If the JRun server hangs or fails, ClusterCATS attempts to recover the failed service. When the JRun service is recovered, the probe can restart the JRun server and begin sending HTTP traffic to it again.

This section describes the following:

Configuring JRun probes in Windows

This section describes the following:

Adding JRun probes

ClusterCATS lets you set up one probe monitor for each server in a cluster. Each monitor can have multiple probes associated with it. As a result, clusters typically have multiple probe monitors (one for each server), and each monitor may have one or more probes.

The procedure for adding a new monitor and probe is different from adding a probe to a server that already has a probe monitor. This section describes how to perform both activities.

Note:   The JRun service must be running on your server to add a probe.

To add a new monitor and JRun probe:

  1. Open the ClusterCATS Explorer and select a server.
  2. Select Server > New Monitor or right-click the server and select New Monitor.

    The New Monitor dialog box appears:

    New Monitor dialog box

  3. Enter a name to assign to this probe's monitor in the Name field on the New Monitor dialog box and click OK.

    The monitor's Properties dialog box appears:

    Monitor Properties dialog box

  4. Click the New Probe button The New Probe button .

    The JRun Application Probe settings dialog box appears:

    JRun Application Probe settings dialog box

  5. Configure the application probe settings as described in the following table:
    Field
    Description
    Web Server
    Select the name of the server from the drop-down list.
    Pathname
    Enter the absolute path to the JRun probe. Do not change the default selection unless you installed JRun to a directory other than the default installation directory.
    Working directory
    Enter the absolute path to the probe's working directory. Do not change the default selection unless you installed JRun to a directory other than the default installation directory.
    Startup parameters
    Enter parameters passed to the probe on execution using the following syntax:
    URL success_string [RESTART|NORESTART|
<JRun_server>] [LOG|NOLOG]
    URL - enter the actual URL of the page you want the probe to test. By default, this is http://<your_server>/btauxdir/jrunprobe.jsp. The probe opens the page and searches for the success_string.
    success_string - enter a text string that appears at the page specified by the URL. If the success_string includes spaces, it must be enclosed in quotation marks.
    RESTART|NORESTART - enter RESTART to make the probe automatically restart the default JRun server on probe failure. Enter NORESTART if you do not want ClusterCATS to restart the JRun server on a failure. If you installed JRun as a service, replace RESTART with Service-<service_name> to restart a particular service, or replace RESTART with the name of a specific JRun server (such as admin) to restart.
    LOG|NOLOG - enter LOG to enable logging for the ClusterCATS application probe or NOLOG to disable it. The probe logs are stored in the /<CC_install_directory>/log/ directory.
    The default for Startup Parameters is http://<your_server>/btauxdir/jrunprobe.jsp Hello NORESTART NOLOG
    Timeout (sec)
    Enter a time to indicate how long ClusterCATS waits before a JRun server failure is registered.
    Do not set this value to less than 60 seconds, because ClusterCATS may restart the JRun server inadvertently (due to network congestion, for example), rather than detect an actual failure on the JRun server.
    Frequency (sec)
    Enter a time to indicate how often the probe checks the JRun server.
    Probes that restart web applications should be configured to run no more frequently than the time it takes to stop and restart JRun. This is highly site-specific, because it depends on system resources available on servers and the volume of traffic at a site.
    For probes that do not restart the web application, the frequency depends on how long you can reasonably afford to have your web application offline. A minimum frequency of 15 seconds is recommended.
    Return value
    Enter 0 to make a probe succeed on a successful probing of the page. Enter a non-zero number to make a probe succeed on a failure.
    The default is 0. Only under rare circumstances would you change this to a non-zero number.
  6. Click Register to create the probe.
  7. Close all open dialog boxes.

    Icons for the monitor and probe appear under the Monitor Manager in the ClusterCATS Explorer.

To add a new probe to an existing probe monitor:

  1. In the ClusterCATS Explorer, select the cluster_name > Monitor Manager > monitor_name in the left pane.
  2. Select Monitor > Properties.

    The monitor's Properties dialog box appears:

    Monitor Properties dialog box

  3. Click the New Probe button The New Probe button .

    The JRun Application Probe settings dialog box displays.

  4. Configure the application probe settings as described in the table in "Using JRun probes".
  5. Click Register to create the probe.
  6. Close all open dialog boxes.

    An icon for the new probe appears under the Monitor Manager in the ClusterCATS Explorer.

Removing JRun probes

To remove a JRun probe:

  1. Open the ClusterCATS Explorer.
  2. Select the cluster_name > Monitor Manager > monitor_name > probe_name in the left pane.
  3. Select Probe > Delete or right-click the probe and select Delete.

Configuring JRun probes in UNIX

This section describes the following:

Adding JRun probes

To add a new JRun probe:

  1. In the ClusterCATS Web Explorer, click the Show Cluster link.

    The Show Cluster page appears.

  2. In the Web Server Name field, enter the fully qualified host name of a server for which to configure the JRun probe.
  3. Click OK.

    The Cluster Member List page appears.

  4. Click the Server Attributes link.

    The Connect To Server page appears.

  5. Select a server to add a probe to from the Web Server Name list box.
  6. Click OK.

    The selected server's Properties page appears.

  7. Click the JRun Probe link.

    If there are probes for this server, the Probe List page appears:

    Probe List page

  8. To create a new probe, click New. The JRun Application Probe page appears.

    If this is the first probe for this server, or you clicked New to add a probe, the JRun Application Probe page appears:

    JRun Application Probe page

  9. Configure the application probe settings as described in the following table:
    Field
    Description
    Status
    This is an informational field. If the probe is not registered, the Status displays Not registered. If the probe is registered, the Status displays Succeeding.
    Pathname
    Enter the path to the JRun probe. Do not change the default selection unless you installed ClusterCATS for JRun to a directory other than the default installation directory. The default is /usr/lib/btcats/program/jrunprobe.
    Working directory
    Enter the path to the probe's working directory. Do not change the default selection unless you installed ClusterCATS for JRun to a directory other than the default installation directory.
    The default is /usr/lib/btcats/program/.
    Startup Parameters
    Enter parameters passed to the probe on execution, using the following syntax:
    URL success_string [RESTART|NORESTART|
<JRun_server>] [LOG|NOLOG]
    URL - enter the actual URL of the page you want the probe to test. By default, this is http://<your_server>/btauxdir/jrunprobe.jsp. The probe opens the page and searches for the success_string.
    success_string - enter a text string that appears at the page specified by the URL. If the success_string includes spaces, it must be enclosed in quotation marks.
    RESTART|NORESTART - enter RESTART to make the probe automatically restart the default JRun server on a failure. Enter NORESTART if you do not want ClusterCATS to restart the JRun server on a failure. You can replace RESTART with the name of a specific JRun server (such as default) to restart.
    LOG|NOLOG - enter LOG to enable logging for the ClusterCATS application probe or NOLOG to disable it. The probe logs are stored in the /<CC_install_directory>/log/ directory.
    The default for Startup Parameters is http://<your_server>/btauxdir/jrunprobe.jsp Hello NORESTART NOLOG
    Timeout (sec)
    Enter a time to indicate how long ClusterCATS waits before a JRun server failure is registered.
    Do not set this value to less than 60, because ClusterCATS might restart the JRun server inadvertently (due to network congestion, for example), rather than detect an actual failure on the JRun server.
    Frequency (sec)
    Enter a time to indicate how often the probe checks the JRun server.
    Probes that restart web applications should be configured to run no more frequently than the time it takes to stop and restart JRun. The time is highly site-specific, because it depends on the system resources available on the servers and the volume of traffic at the site.
    For probes that do not restart the web application, the frequency depends on how long you can reasonably afford to have your web application offline. A minimum frequency of 15 seconds is recommended.
    Return value
    Enter 0 to make the probe succeed on a successful probing of the page. Enter a non-zero number to make the probe succeed on a failure.
    The default is 0. Only under rare circumstances would you change this to a non-zero number.
  10. Click Register to create the probe. ClusterCATS begins to test the selected server immediately.

Editing and removing JRun probes

To edit or remove a JRun probe:

  1. In the ClusterCATS Web Explorer, click the Show Cluster link.

    The Show Cluster page appears.

  2. Enter the fully qualified host name of a server for which to configure the JRun probe in the Web Server Name field.
  3. Click OK.

    The Cluster Member List page appears.

  4. Click the Server Attributes link.

    The Connect To Server page appears.

  5. Select the server that hosts the probe in the Web Server Name list box.
  6. Click OK.

    The selected server's Properties page appears.

  7. Click the JRun Probe link.

    The Probe List page appears.

  8. Select the probe to edit or remove.
  9. To remove the probe, click Delete.

    ClusterCATS removes the JRun probe.

  10. To edit the probe, click Edit.

    A page with all the available probes appears.

  11. Edit the fields corresponding to the probe that you want to change, and click Register.
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