'mysql' => [
 'driver' => 'mysql', 
 'write' => [ 
 'host' => '192.168.1.180', 
 ], 
 'read' => [
 ['host' => '192.168.1.182'], 
 ['host' => '192.168.1.179'], 
 ],
 ... 
]

'mysql' => [
 'driver' => 'mysql', 
 'write' => [ 
 'host' => '192.168.1.180', 
 ], 
 'read' => [
 'host' => ［
 '192.168.1.182',
 '192.168.1.179'
 ], 
 ],
 ... 
]

'mysql' => [
 'driver' => 'mysql', 
 'write' => [ 
 'host' => '192.168.1.180', 
 'username' => 'write',
 'password' => 'write',
 ], 
 'read' => [
 [
 'host' => '192.168.1.182',
 'username' => 'read1',
 'password' => 'read1',
 ], 
 [
 'host' => '192.168.1.179',
 'username' => 'read2',
 'password' => 'read2',
 ], 
 ],
 ... 
]

'mysql' => [
 'driver' => 'mysql', 
 'write' => [ 
 'host' => '192.168.1.180', 
 'username' => 'write',
 'password' => 'write',
 ], 
 'read' => [
 'host' => ［
 '192.168.1.179',
 '192.168.1.182',
 ],
 'username' => 'read',
 'password' => 'read', 
 ],
 ... 
]

'mysql' => [
 'driver' => 'mysql', 
 'write' => [ 
 'host' => '192.168.1.180', 
 'username' => 'write',
 'password' => 'write',
 ], 
 'read' => [
 'host' => '192.168.1.179'
 'username' => 'read',
 'password' => 'read', 
 ],
 ... 
]

class ConnectionFactory
{
 ...

 /**
 * Get the read configuration for a read / write connection.
 *
 * @param array $config
 * @return array
 */
 protected function getReadConfig(array $config)
 {
 $readConfig = $this->getReadWriteConfig($config, 'read');

 if (isset($readConfig['host']) && is_array($readConfig['host'])) {
 $readConfig['host'] = count($readConfig['host']) > 1
 "dot" notation.
 *
 * @param array $array
 * @param array|string $keys
 * @return void
 */
 public static function forget(&$array, $keys)
 {
 $original = &$array;
 
 $keys = (array) $keys;
 
 if (count($keys) === 0) {
 return;
 }
 
 foreach ($keys as $key) {
 $parts = explode('.', $key);
 
 while (count($parts) > 1) {
 $part = array_shift($parts);
 
 if (isset($array[$part]) && is_array($array[$part])) {
  $array = &$array[$part];
 } else {
  $parts = [];
 }
 }
 
 unset($array[array_shift($parts)]);
 
 // clean up after each pass
 $array = &$original;
 }
 }
 
 ...
}