Resource attributes

Global Traffic Management balances load based on three attributes of a resource:
  • current load
  • target load
  • capacity
These attributes are continuously reported to GTM by mechanisms described here. These attributes are measured and reported separately for each data center.

The current load is the current load on the resource. The target load can be thought of as a soft limit, and the capacity as a hard limit, on load.

The system optimizes traffic so that all data centers have a current load below the target load, to the extent that it's possible.

Load balancing begins when the current load for a resource in a data center exceeds the target load. If that happens, GTM tries to reduce the load sent to that data center by shifting some of the load to other data centers that are not exceeding their targets. To maintain a user’s peak performance, GTM selects users that are least negatively affected by the shift. As an example, assume there are data centers in New York and Singapore. If the New York data center is over target, GTM might shift a user in London to the Singapore data center in preference to shifting a user in New York, as the shift would be more detrimental to the performance of the New York user than it would to the performance of the London user.

Information about traffic load on your resources can be sent to GTM in the following ways:
  • XML load objects
  • Non-XML load objects
  • Liveness test download scores