FRONTEND_MVC/config/db.php

<?php

$db = [
    'class' => 'yii\db\Connection',
    'dsn' => 'mysql:host=amic-mysql;dbname=amic_new',
    'username' => 'work',
    'password' => 'work',
    'charset' => 'utf8',

    // Schema cache options (for production environment)
    //'enableSchemaCache' => true,
    //'schemaCacheDuration' => 60,
    //'schemaCache' => 'cache',
];
$enableSlaves = true;
$slavesrv = 'mysql:host=192.168.1.4;port=3307;dbname='.DB_NAME; //slave с распределение нагрузки

/*
		Привышение нагрузки
*/
if( file_exists('/.data2/status/cache_on.fl') ){
	$slavesrv = 'mysql:host=192.168.1.3;port=3306;dbname='.DB_NAME;		//все на slave
}

/*
		Падение реплики
*/
if( file_exists('/home/admin/www-bot/replica-stop_192.168.1.3.fl') ){ //реплика упала
	$enableSlaves = false;
}

if(defined("DB_DSN")){
    $port = "";
    if(defined("DB_PORT") && DB_PORT!=="") $port = ";port=".DB_PORT;
    $db = [
        'class' => 'yii\db\Connection',
        'dsn' => 'mysql:host='.DB_DSN.$port.';dbname='.DB_NAME,
        'username' => DB_USER,
        'password' => DB_PASSWORD,
        'charset' => 'utf8mb4',
        // Schema cache options (for production environment)
        'enableSchemaCache' => true,
        'schemaCacheDuration' => 60,
        'schemaCache' => 'cache',
		'enableSlaves' => $enableSlaves,
		'slaveConfig' => [
        'username' => DB_USER,
        'password' => DB_PASSWORD,
        'attributes' => [
            // используем небольшой таймаут для соединения
            PDO::ATTR_TIMEOUT => 10,
			],
		],
// список настроек для подчинённых серверов
    'slaves' => [
			['dsn' => $slavesrv ],
		],
    ];
}
return $db;