Front end task - Predictive Load Balancing

Web server configuration example from a Well House Consultants training course
More on Web server configuration [link]

This example is described in the following article(s):
• Predictive Load Balancing - PHP and / or Java - [link]

This example references the following resources:
http://www.wellho.net/mouth/1938_.html

Source code: frontend Module: H305

<?php

/* This is the code to run on a single front end
server for a major website that spreads a certain
task over a number of back end systems (three in
this example). Rather than using a standard
Apache module for the balancing, we have implemented
the algorithm ourselves using loading information
fed back by the back end processes once they're
predicted how much work will be involved in a
particular task they have been passed. */

# See also http://www.wellho.net/mouth/1938_.html

$servers = array("wilfred","duncan","nick");

# Look for current loadings

# Algorithm applicable to first contact in a session
# Alternative algorithm to be used if contact is
# identified as an ongoing session.

$current = array("wilfred" => 0); # Seeding
mysql_pconnect("frontend","trainee","abc123");
mysql_select_db("test");
$qs = mysql_query("select size, name from actives");
while ($row = mysql_fetch_assoc($qs)) {
        $current[$row[name]] += $row[size];
        }

# Sort loadings and get lightest
asort ($current);
$inorder = array_keys($current);
$target = $inorder[0];

# Also needed - occasional call to delete records that
# are over (say) 30 seconds old from the load database
# - just in case a connection is lost / back end fails
# to complete.

# Run the request on the appropriate backend
# Need to deal with cookies, POST method, etc!
$result = file_get_contents
        ("http://$target/action.php?$_SERVER[QUERY_STRING]");
print $result;
?>

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