Resource attributes

Global Traffic Management balances load based on three attributes of a resource:
  • Current – This is the current load on the resource.
  • Target – This is the point at which load shifting should begin. Think of this as a soft limit on load.
  • Capacity – This indicates the capacity of the resource. Think of this as a hard limit on load.

These attributes are measured separately for each data center, and they are continuously reported to GTM by the mechanisms described below.

GTM optimizes traffic to ensure that all data centers have a current load below the target load, if possible, and to prevent current load from exceeding capacity.

Load shifting 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 the load to other data centers that are not exceeding their target load.

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 exceeds its target load, GTM might shift a user in London to the Singapore data center as opposed 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.

Akamai recommends that you adhere to the following resource attribute guidelines:
  • Do not calculate load values manually, as this might result in poor performance. The load object must not be a static file on disk that is edited on demand. If a data center needs to be removed from consideration, you should take one of the following actions:
    • Mark the data center as disabled using the Akamai Control Center.
    • Mark the data center as disabled using the API.
    • Cause the liveness test for the data center to fail.
  • Do not set the target load to be the same as the capacity. GTM works hard to keep load below capacity, and allows load to be close to the target.
  • Do not change the capacity unless the hardware or software of the data center itself changes, thereby changing the maximum number of requests that the data center can handle.
  • The current, target, and maximum load values must be non-negative and less than 2^31 (2,147,483,647).
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