premise:
mysql: A machine
Application: B-machine
I set up a cross-domain access environment and access my local mysql database on another machine, but I can't connect all the time and report a 2003 error. There is no problem with mysql authorization checks. I suddenly thought, can I ping it, A I can ping B, but B can't ping A. I saw that it was a problem with the win7 firewall. Then I turned off A's firewall, and then B pinged A. It reported that the target host could not be found, and then B's firewall was turned off. Closed, then the ping is smooth, and the DB connection is smooth.
Lesson: DB failure may not be the problem of mysql, let's look at the network first