[google-cloud-sql-discuss] Does CloudSQL MySQL block client access?

This is a cross post from cloudsql channel in GCP Slack, but I have not received any response yet. So, please allow me to post it here too.

https://googlecloud-community.slack.com/archives/C0H0GRV39/p1590525710126000

Hello. I tested if Cloud SQL MySQL (version 5.7) blocks access from its clients when the number of connection related errors exceeds the value of `max_connect_errors` variable.

I used "echo | nc -v X.X.X.X 3306" from my workstation and a VM in GCP against a publicly accessible Cloud SQL MySQL instance (X.X.X.X is the server IP address).  I did this to simulate an incomplete handshake, but the instance didn't block access from the sources; even though the number of failed handshakes exceeded the max_connect_errors value.

I did the same testing against an existing on-premise MySQL instance and another instance built from source code (5.7.25).  I confirmed it blocked access on the client side from sources that reached max_connect_errors.  It gave the message, "Host 'Y.Y.Y.Y' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'".

I noticed there was no entry in performance_schema.host_cache table even after upgrading the machine type to db-n1-highmem-4, which is a requirement to enable performance_schema.

So, I am wondering if Google dropped the host blocking logic from Cloud SQL MySQL. I searched GCP docs, but couldn't find any. Does anybody have information about host blocking in Cloud SQL MySQL?

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