我已经在谷歌云应用引擎部署codeigniter项目.我试图通过codeigniter连接gcloud mysql.获取数据库连接问题.数据库连接示例如下-

public $default = [
        'DSN'      => 'mysql:dbname=db_name;unix_socket=/cloudsql/project:region:instance',
        'hostname' => 'public_ip',
        'username' => 'username',
        'password' => 'password',
        'database' => 'db_name',
        'DBDriver' => 'MySQLi',
        'DBPrefix' => 'tbl',
        'pConnect' => false,
        'DBDebug'  => (ENVIRONMENT !== 'production'),
        'charset'  => 'utf8mb4',
        'DBCollat' => 'utf8_general_ci',
        'swapPre'  => '',
        'encrypt'  => false,
        'compress' => false,
        'strictOn' => false,
        'failover' => [],
        'port'     => 3306,
    ];

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示例的连接IP是否授权？
我得到了Main connection [MySQLi]: Connection timed out
我试过不同的方法