instruction: Create a Dockerfile for configuration
output: ```dockerfile
  from
  standard input.
  
  $ openssl rand -base64 20 | docker secret create mysql_password -
  
  l1vinzevzhj4goakjap5ya409
  The value returned is not the password, but the ID of the secret. In the
  remainder of this tutorial, the ID output is omitted.Generate a second secret for the MySQL root user. This secret isn't
  shared with the WordPress service created later. It's only needed to
  bootstrap the mysql service.
  
  $ openssl rand -base64 20 | docker secret create mysql_root_password -
  List the secrets managed by Docker using docker secret ls:
  
  $ docker secret ls
  
  ID NAME CREATED UPDATED
  l1vinzevzhj4goakjap5ya409 mysql_password 41 seconds ago 41 seconds ago
  yvsczlx9votfw3l0nz5rlidig mysql_root_password 12 seconds ago 12 seconds ago
  The secrets are stored in the encrypted Raft logs for the swarm.Create a user-defined overlay network which is used for communication
  between the MySQL and WordPress services. There is no need to expose the
  MySQL service to any external host or container.
  
  $ docker network create -d overlay mysql_private
  Create the MySQL service. The MySQL service has the following
  characteristics:Because the scale is set to 1, only a single MySQL task runs.
  Load-balancing MySQL is left as an exercise to the reader and involves
  more than just scaling the service.Only reachable by other containers on the mysql_private network.Uses the volume mydata to store the MySQL data, so that it persists
  across restarts to the mysql service.The secrets are each mounted in a tmpfs filesystem at
  /run/secrets/mysql_password and /run/secrets/mysql_root_password.
  They are never exposed as environment variables, nor can they be committed
  to an image if the docker commit command is run. The mysql_password
  secret is the one used by the non-privileged WordPress container to
  connect to MySQL.Sets the environment variables MYSQL_PASSWORD_FILE and
  MYSQL_ROOT_PASSWORD_FILE to point to the
  files /run/secrets/mysql_password and /run/secrets/mysql_root_password.
  The mysql image reads the password strings
  ```