Using ClusterCATS
Configuring Clusters

Server load thresholds

ClusterCATS ensures that your web applications remain available and running at optimum performance by intelligently managing the HTTP traffic hitting your clustered servers. By setting load thresholds on each server in your cluster, you can control and manage your site's availability and performance. Many of your threshold configuration decisions hinge on your site's architecture and where the bulk of your processing resources must be allocated.

During an HTTP redirection, ClusterCATS evaluates the cluster's state according to the HTTP server state first, and then the JRun/ColdFusion server load. This policy is the same in centralized and distributed ClusterCATS configurations. In a centralized ClusterCATS cluster with all web servers at one site, ClusterCATS redirects only if the server is busy or restricted.

For each cluster member, you configure two load thresholds:

• Peak load threshold - the maximum load the server can handle before its performance degrades significantly or becomes unavailable.
• Gradual redirection threshold - the point at which HTTP requests begin to be redirected to other less-loaded members in a cluster so the server's performance does not degrade or become unavailable.

By default, the peak load threshold is 90% and the gradual redirection threshold is 10%. These default settings adequately handle HTTP traffic going across most websites. However, if your website is particularly processing intensive, you should lower both threshold settings to better accommodate the increased load.

If you want the server to handle as much load as possible, set the threshold values close to one another. However, if you want redirection to occur well in advance of the server nearing its peak threshold, set the values farther apart so there is a difference of at least 10% between the two threshold values.

This section shows you how to set the peak and gradual redirection load thresholds for ClusterCATS Servers in the following sections:

• "Configuring load thresholds in Windows"
• "Configuring load thresholds on UNIX"

Configuring load thresholds in Windows

To adjust load thresholds for a cluster member:

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

   The server's Properties dialog box appears:

   

3. Click the Load tab.

   

4. Enter a numeric value (less than 100%) in the first Load Management field. This is referred to as the peak load threshold. In the example above, the peak load threshold is set to 90.
5. Enable the Gradual Redirection check box.
6. Enter a new value in the Gradual Redirection field. This value must be lower than the peak load threshold.
7. Click OK to apply your new threshold settings.

Viewing a cluster's load status

JRun/ColdFusion reports its load data directly to ClusterCATS. You can view the load on the servers at any time using the Server Load Monitor.

To view your cluster's current load levels:

1. Open the ClusterCATS Explorer and select a cluster.
2. Select Monitor > Load or right-click the cluster you have selected and select Monitor > Load.

   The Server Loads dialog box appears, showing the current load status for each cluster member in the cluster that you selected:

   

   The load monitor shows three lines:

   • Top line (red): Peak load threshold
   • Middle line (yellow): Gradual Redirection load threshold
   • Bottom line (green): JRun/ColdFusion server load

Adjusting load threshold settings graphically

You can view and set threshold settings of a cluster member using the Server Load Monitor's visual display. To set or change threshold settings, use the mouse to drag the Peak (red) and Gradual Redirection (yellow) threshold lines to their settings instead of entering numeric values in fields

To configure load threshold settings using the Server Load dialog box:

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

   The Server Load dialog box appears:

   

3. Use your mouse to drag the peak load threshold (red) up or down.

   As you move the line, the peak load threshold percentage changes.

4. Enable gradual redirection by selecting the Gradual Redirection check box.
5. Drag the Gradual Redirection load threshold (yellow) to adjust it accordingly.
6. Close the dialog box to apply the load threshold settings you configured.

Configuring load thresholds on UNIX

To configure load thresholds for a cluster member:

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 in the Web Server Name field.
3. Click OK.

   The Cluster Member List page appears. If you get an "Error: Server <cluster_member_name> could not be found", ensure that you used the correct, fully qualified server name and that the server is running.

   

4. Click the Server Attributes link.

   The Connect To Server page appears:

   

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

   The selected server's Server Properties page appears:

   

7. Click the Administration link under Server Attributes.

   The Server Administration page appears for the selected server:

   

8. To change the peak load threshold, enter a new numeric value (less than 100%) in the Standard Load Threshold field.
9. Enable the Gradual Redirection check box if it is not already enabled.
10. To change the Gradual Redirection load threshold, enter a new numeric value in the Gradual Load Threshold field. This value must be lower than the standard load threshold.
11. Click OK to apply your new load threshold settings.

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