Load object formats

This help section discusses XML and non-XML custom load objects.

A custom load object file is an XML or plain text file that provides real-time information about the load of each resource.

Resources can constrain multiple properties only if you are using XML load objects.

When you configure Global Traffic Management to use load feedback based on an XML or non-XML load object, GTM periodically fetches a fresh load object using HTTP or HTTPS. By default, GTM fetches the load object every 30 seconds.

The load object must be accurate, timely, and available. If it is inaccurate, GTM cannot balance the load correctly. If it is untimely, meaning that the load data it reports is not current, load oscillations can occur because GTM cannot detect soon enough the results of load balancing decisions it makes.

The load objects for all data centers in a property must be configured with the same update interval, and must have their load updated at approximately the same time. The best practice is to match the load object refresh interval (how often GTM fetches the load object).

If the load objects for all data centers in a property are not updated at approximately the same time, some data centers might appear to be able to take more traffic without a load increase, while others might appear to have load increase quickly. This can result in oscillations.

If the load object is unavailable, GTM continues to use the most recent load data it successfully fetched. Examples of reasons why the load object is unavailable include HTTP GET failures, the script throwing an error, or the server refusing connections.

You must configure GTM to fetch a load object for each data center from a server you define. Use Control Center to configure one or more load servers for each data center by specifying the following information:
  • The name or IP address of the load server(s)
  • The relative URL of the load object
  • Whether to use HTTP or HTTPS to fetch a load object
It's acceptable if the load object contains load information for other data centers; the extra information is ignored.