Do you need to change the password of a MySQL user that it's being used in an application, and can't allow a single downtime? Well, MySQL 8.0.14 came with a feature called Dual Password Support, with it you can change the password keeping the previous password as a kind of backup. That way you still can log in using the old password or can start using the new one. With that, the password change workflow it's the following.
1) Change password keeping the old one;
2) Deploy the new config to your app/cluster;
3) Discard the old password.
To change the password and keep the old one, you have the following command.
ALTER USER 'appuser'@'localhost' IDENTIFIED BY 'new_password' RETAIN CURRENT PASSWORD;
To discard the old one, run the following.
ALTER USER 'appuser'@'localhost' DISCARD OLD PASSWORD;
And you are done. Hope you find it as useful as I :)