TCP health checks to port 3306 quickly exceed max_connect_errors

Context

We have a MariaDB Galera setup with load balancing configured to each of the MariaDB nodes in the cluster. We want to achieve a simple production-like experience.

In order for the load balancer to work properly, it is using a TCP health check to port 3306 for all nodes to check if they are up, succeeding if it is open. We're using Azure's health check service for TCP ports, and in our case this is performed each 5 seconds.

Description of the issue

Since 10.4, each TCP health check to port 3306 is causing a warning to be added to the logs, i.e.:

2019-12-31 11:58:10 24 [Warning] Aborted connection 24 to db: 'unconnected' user: 'unauthenticated' host: '127.0.0.1' (This connection closed normally without authentication)

This can be reproduced with the following command in the instance running the MariaDB 10.4 server:

echo exit | telnet 127.0.0.1 3306

This log disappears when setting "log_warning=1", which used to be the default value for the parameter prior to the 10.2.4 release (see "Configuring the error log verbosity").

This warning was implemented as part of MDEV-19282, where it was mentioned that level 2 in "log_warning" should also include aborted connections. It was also suggested to configure logrotate to avoid it getting too big.

We ask if you can consider increasing the required "log_warning" level for the warning to be triggered, to a value such as 3, since TCP port checks are a rather common action for a warning to appear each time.