使用TCP从App Engine自定义环境连接到Google Cloud SQL时出错

# app.yaml
network:
  name: your-vpc-network
  subnetwork: your-subnetwork

gcloud projects add-iam-policy-binding your-project-id \
    --member serviceAccount:your-service-account@your-project-id.iam.gserviceaccount.com \
    --role roles/cloudsql.client

gcloud compute firewall-rules create allow-cloudsql-access \
    --allow tcp:3306 \
    --target-tags=your-target-tag \
    --source-ranges=YOUR_APP_ENGINE_IP_RANGE

gcloud sql instances patch your-instance-name \
    --authorized-networks=YOUR_APP_ENGINE_IP_ADDRESS

import pymysql

# 连接参数
config = {
    'user': 'your-username',
    'password': 'your-password',
    'host': 'your-cloud-sql-ip',
    'database': 'your-database',
    'port': 3306,
    'charset': 'utf8mb4',
    'cursorclass': pymysql.cursors.DictCursor
}

try:
    connection = pymysql.connect(**config)
    with connection.cursor() as cursor:
        sql = "SELECT * FROM your_table"
        cursor.execute(sql)
        result = cursor.fetchall()
        print(result)
finally:
    connection.close()