From time to time i receive this error while running the official mysql image in docker:
An exception occured in driver: SQLSTATE[HY000]  Host ‘172.17.0.5’ is
not allowed to connect to this MySQL server
The reason for this is not quite clear yet but i usually resolve it like described here.
Note that all data stored in the project will be lost!
So this error is quite annyoing but luckily i work on fixtures so i can restore data easily.
These steps let me connect to the mysql container again, at least.