GRANT ALL PRIVILEGES ON testdb_development.* TO 'rails_user'@'localhost' IDENTIFIED BY 'test';

adapter: mysql2
encoding: utf8
pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
username: rails_user
password: test
host: localhost

rails db:schema:dump

rails aborted!
Mysql2::Error: Access denied for user 'rails_user'@'172.20.0.1' (using password: YES)