You can access the Adaptive Parameters in the LoadMaster Web User Interface (WUI) by going to Rules & Checking > Check Parameters. The Adaptive Parameters section only shows on this screen if the Scheduling Method of at least one Virtual Service is set to resource based (adaptive).

Adaptive Interval (sec)

This is the interval, in seconds, at which the LoadMaster checks the load on the servers. A low value means the LoadMaster is very sensitive to load, but this comes at a cost of extra load on the LoadMaster itself. 7 seconds is a good starting value. This value must not be less than the HTTP checking interval.

Adaptive URL

The Adaptive method retrieves load information from the servers using HTTP inquiry. This URL specifies the resource where the load information of the servers is stored. This resource can be either a file or program (for example Adaptive Agent) that delivers this information. The standard location is /load. It is the server's job to provide the current load data in this file in ASCII format. In doing so, the following must be considered:

An ASCII file containing a value in the range of 0 to 100 in the first line where 0=idle and 100=overloaded. As the number increases, that is, the server becomes more heavily loaded, the LoadMaster will pass less traffic to that server. Hence, it 'adapts' to the server loading.

If the server becomes 101% or 102% loaded, a message is added to the logs.

The file is set to /load by default.

The file must be accessible using HTTP.

The URL must be the same for all servers that are to be supported by the adaptive method.

Note: This feature is not only of interest for HTTP-based Virtual Services, but for all Services. HTTP is merely used as the transport method for extracting the application-specific load information from the Real Server.

Port

This value specifies the port number of the HTTP daemon on the servers. The default value is 80.

Note: Port 443 will not work.

Min. Control Variable Value (%)

This value specifies a threshold below which the balancer will switch to static weight-based scheduling, that is, normal Weighted Round Robin. The value is a percentage of the maximum load (0-50). The default and the minimum value is 5. The minimum is 5 because if it is below 5 it would be better to use weighted round robin.

An example scenario of when adaptive scheduling is applied is as follows:

  • There are two Real Servers, adaptive scheduling is selected, and the Min. Control Variable Value is set to 30.

  • If the agent returns a value < 30, the scheduling is treated as weighted round robin.

  • If the agent returns a value of > 30, the scheduling is treated as adaptive.