mysqlctld is a gRPC server that can be used instead of the mysqlctl client tool. If the target directories are empty when it is invoked, it automatically performs initialization operations to bootstrap the mysqld instance before starting it. The mysqlctld process can subsequently receive gRPC commands from a vttablet to perform housekeeping operations like shutting down and restarting the mysqld instance as needed.
mysqld_safe is not used so the mysqld process will not be automatically restarted in case of a failure.
To enable communication with a vttablet, the server must be configured to receive gRPC messages on a unix domain socket. For example: