Advisors

Advisors periodically open a TCP connection with each server and send a request message to the server. The content of the message is specific to the protocol running on the server. For example, the HTTP advisor sends an HTTP “HEAD” request to the server.

Advisors then listen for a response from the server. After getting the response, the advisor makes an assessment of the server. To calculate this “load” value, most advisors measure the time for the server to respond, and then use this value (in milliseconds) as the load.

Advisors then report the load value to the manager function, where it appears in the manager report in the “Port” column. The manager then calculates aggregate weight values from all its sources, per its proportions, and sets these weight values into the executor function. The Executor will then use these weights for load balancing new incoming client connections.

If the advisor determines that a server is alive and functioning properly, it will report a positive, non-zero load number to the Manager. If the advisor determines that a server is not active, it will return a special load value of negative one (-1). The Manager and the Executor will not forward any further connections to that server until that server has come back up.
Note: Before sending the initial request message, the advisor will ping the server. This is intended to provide quick status to determine if the machine is online. After the server responds to the ping, no more pings are sent. To disable the pings, add -DLB_ADV_NB_PING to the Load Balancer start script file.
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Last updated: September 12, 2012 11:41 PM EDT
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