CallbackIterator.php

<?php declare(strict_types=1);

class CallbackIterator implements Iterator
{
    private $index = 0;
    private $maxIterations = 0;
    private $callback;
    
    public function __construct(int $anIterationCount, callable $aCallback)
    {
        $this->maxIterations = abs($anIterationCount);
        $this->callback      = $aCallback;
    }
    
    public function current()
    {
        return $this->callback();
    }
    
    public function next()
    {
        ++$this->index;
    }
    
    public function key() : int
    {
        return $this->index;
    }
    
    public function valid() : bool
    {
        return $this->maxIterations > $this->index;
    }
    
    public function rewind()
    {
        $this->index = 0;
    }
}

connection.php

<?php declare(strict_types=1);

$connection = null;
$instanceId = $configuration->getProperty("db.master.instanceId");
$dsn        = buildDsn(
    $configuration->getProperty("db.master.database"),
    $endpointManager->getEndpoint($instanceId)
);

$iterator = new CallbackIterator(5, function() use ($dsn, $connectionManager) {
    return $connectionManager->connect($dsn);
});

while ($connection === null && $iterator->valid()) {
    try {
        $log->debug("Connecting [$instanceId]");
        $connection = $iterator->current();
    } catch (ConnectionException $ce) {
        $log->debug("Failed to connect [$instanceId]");
        $log->error($ce->getMessage());
        $log->error($ce->getTraceAsString());
    }
    $iterator->next();
}
if ($connection === null) {
    throw ConnectionException::failure($instanceId);
}

function buildDsn(string $aDatabaseName, Endpoint $anEndpoint) : string
{
    $cdn  = ($anEndpoint->hasReplicas()) ? buildReplicaDsn($anEndpoint) : buildEndpointDsn($anEndpoint);
    $cdn .= "/" . $aDatabaseName;
    return $cdn;
}

function buildEndpointDsn(Endpoint $anEndpoint) : string
{
    return "mysql://" . $anEndpoint->getUri();
}

function buildReplicaDsn(Endpoint $anEndpoint) : string
{
    $cdn = "mysql:replication://" . $anEndpoint->getUri();
    /** @var $replica Endpoint */
    foreach ($anEndpoint->getReplicas() as $replica) {
        $cdn .= "," . $replica->getUri();
    }
    return $cdn;
}