Use a node alias instead of the ip:port pair when calculating the hash of a node in a cluster with Predis.

AliasBasedHashRing.php

<?php

namespace Nrk;

use Predis\Distribution\HashRing;

// NOTE: this class won't work with a version of Predis prior to commit b30f495

class AliasBasedHashRing extends HashRing {
    public function add($node, $weight = null) {
        $parameters = $node->getParameters();
        if (!$parameters->isSetByUser('alias')) {
            throw new \InvalidArgumentException(
                "The 'alias' property must be set for {$node} to use " .
                "this kind of distribution strategy"
            );
        }
        parent::add($node, $weight);
    }

    protected function getNodeHash($nodeObject) {
        return $nodeObject->getParameters()->alias;
    }
}

NOTES.md

See this article and this issue for more details about the Nrk\AliasBasedHashRing class and the reasons behind it.

test_alias_based_hashring.php

<?php

require 'autoload.php';
require 'AliasBasedHashRing.php';

use Predis\Network\PredisCluster;
use Nrk\AliasBasedHashRing;

// ------------------------------------------------------------------------- //

const UNUSED_DB = 15;

$servers = array(
    array(
        'host'     => '192.168.1.33',
        'port'     => 6379,
        'alias'    => 'node01',
        'database' => UNUSED_DB,
    ),
    array(
        'host'     => '192.168.1.33',
        'port'     => 6380,
        'alias'    => 'node02',
        'database' => UNUSED_DB,
    ),
);

$options = array(
    'cluster' => function() {
        $distributor = new AliasBasedHashRing();
        return new PredisCluster($distributor);
    },
);

// ------------------------------------------------------------------------- //

$client = new Predis\Client($servers, $options);
$node01 = $client->getClientFor('node01');
$node01->flushdb();
$node02 = $client->getClientFor('node02');
$node02->flushdb();

for ($i = 1; $i <= 100; $i++) {
    $client->set("key:$i", str_pad($i, 3, '0', 0));
    $client->get("key:$i");
}

$server1 = $node01->info();
$server2 = $node02->info();
printf("Server '%s' has %d keys while server '%s' has %d keys.\n",
    'first', $server1['db'.UNUSED_DB]['keys'], 'second', $server2['db'.UNUSED_DB]['keys']
);