Coyote Point Systems Equalizer GX Series, Administration Manual

Page: 659 / 866

Server Agents
A server agent is a custom written application that runs on a server and listens on a specific port
(default: 1510). When a connection request is received on that port, the server agent returns an
integer value between -1 and 100 that indicates the relative load on the server (-1 meaning the
server should be considered unavailable, 0 meaning very lightly loaded, and 100 meaning heavily
loaded). Server agents can be used with any cluster type, and have an effect on all load balancing
policies except round robin, which ignores server agent return values.
By default, server agents are disabled on all new server pools. To enable server agents for a
server pool, you need to write the agent, install and run it on each server pool in the cluster, and
then enable server agents for the server pool on Equalizer.
Agent Probe Process
When Equalizer connects to the port on which the server agent is running, it uses the number
returned by the agent in its load balancing calculations, with the server agent policy giving highest
preference to the server agent’s return value over other factors.
The number returned by the agent to Equalizeris intended to indicate the current load on the
server. The agent application that runs on the server can be written in any available scripting or
programming language and can use any appropriate method to determine server load. By default,
the result must be an integer between -1 and 100 returned on the server agent port.
When enabled, server agents should be running on all server instances in the server pool;
however, by default, a server is not marked down when an agent value is not returned.
Equalizercontinues load balancing without the server agent return value unless the health check
instance flag
Require Response
(
require_response
) flag is enabled; if it is, Equalizermust receive
an agent response or the server is marked down.
Copyright © 2014 Coyote Point Systems, A Subsidiary of Fortinet, Inc.
All Rights Reserved. 659
Equalizer Administration Guide