$ docker-compose up --build -d
$ docker exec -it flaskdocker_mysql_1 mysql -u root -p
mysql> CREATE DATABASE flask_docker;
mysql> CREATE USER `flask-docker`@`localhost` IDENTIFIED BY 'pass';
mysql> GRANT ALL PRIVILEGES ON flask_docker.* TO 'flask-docker'@'localhost';
mysql> exit
Bye
$ docker exec -it flaskdocker_web_1 python /usr/src/app/manage.py createdb
# rest of traceback
sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (1045, u"Access denied for user 'flask-docker'@'flaskdocker_web_1.flaskdocker_default' (using password: YES)")

web:
    restart: always
    build: ./app
    volumes:
      - /usr/src/app/static
    expose:
      - "5000"
    environment:
      FLASK_CONFIG: 'production'
    links:
      - mysql:mysql
    command: /usr/local/bin/uwsgi --ini uwsgi.ini

MYSQL_USER = 'flask-docker'
MYSQL_PASS = 'pass'
MYSQL_HOST = 'mysql'
MYSQL_DB = 'flask_docker'
# Database info
SQLALCHEMY_DATABASE_URI = 'mysql+pymysql://{usr}:{passwd}@{host}/{db}'.format(
    usr=MYSQL_USER, passwd=MYSQL_PASS, host=MYSQL_HOST, db=MYSQL_DB
)