FRONTEND_MVC/config/db_old.php

<?php

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

    // Schema cache options (for production environment)
    //'enableSchemaCache' => true,
    //'schemaCacheDuration' => 60,
    //'schemaCache' => 'cache',
];
if(defined("DB_OLD_DSN")){
    $db = [
        'class' => 'yii\db\Connection',
        'dsn' => 'mysql:host='.DB_OLD_DSN.';dbname='.DB_OLD_NAME,
        'username' => DB_OLD_USER,
        'password' => DB_OLD_PASSWORD,
        'charset' => 'utf8',

        // Schema cache options (for production environment)
        //'enableSchemaCache' => true,
        //'schemaCacheDuration' => 60,
        //'schemaCache' => 'cache',
    ];
}
return $db;