为什么 pymysql 连 google cloud sql 报错

代码：
import pymysql

import pymysql.cursors

mydb = pymysql.connect(unix_socket='/cloudsql/projectname:asia-east1:instance-name',
host="x.x.x.x",
user='root',
password='xxxxxxx',
db='databasename',
charset='utf8mb4',
cursorclass=pymysql.cursors.DictCursor)

报错：
pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on 'remotehost' ([Errno 2] No such file or directory)")

环境
python3.7 PyMySQL0.9.3
网络无问题，本地终端可连接