Coyote Point Systems Equalizer Spezifikationen PDF herunterladen (Seite 383)

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 Equalizer is 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. Equalizer continues load balancing without the

server agent return value unless the health check instance flag Require Response (require_response) flag is

enabled; if it is, Equalizer must receive an agent response or the server is marked down.

Sample Server Agent

You can create custom Server Agents as shell scripts, or in Java, Perl, C, or other languages. The code snippet

below is an example of a simple server agent example written in Perl. This code assumes that an integer response

value is supplied on the command line and returns that value when a connection is made on port 1510 (configurable

via the server instance Probe Port (probe_port) variable). This sample agent is intended for testing purposes

only. In a real deployment, the server agent would determine the response value to return by polling system

resources, or some other real-time method.

#!/usr/bin/perl -w

# serveragent.pl

#--------------------

use strict;

use Socket;

# use port 1510 as default

my $port = 1510;

my $proto = getprotobyname('tcp');

# take the server agent response value from the command line

my $response = shift;

# response has to be a valid server agent response

$response==-1 or ($response > 0 and $response<101)

or die "Response must be between -1 and 100";

# create a socket and set the options, set up listen port

socket(SERVER, PF_INET, SOCK_STREAM, $proto) or die "socket: $!";

setsockopt(SERVER, SOL_SOCKET, SO_REUSEADDR, 1) or die "setsock: $!";

my $paddr = sockaddr_in($port, INADDR_ANY);

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