I have created mysql instance v-8.4 in gcp with ssl. But it is not able to connect to app engine. When I connect to mysql using command line in google cloud shell, after that it connects with app engine as well. But as soon as I restart instance, it fails to connect again. I even tried disabling ssl, but it doesnt help and same issue occurs.
There is currently an issue that causes logins to fail when you use the Cloud SQL Auth Proxy to connect to MySQL 8.4 with the caching_sha2_plugin authentication plugin enabled.
We are working on a fix. You can track our progress on the issue here: https://github.com/GoogleCloudPlatform/cloud-sql-proxy/issues/2317
In the mean time, you may work around the issue by configuring the MySQL instance to use the mysql_native_password authentication.