fix(content): harden Docker examples

11_compose/demo/wordpress/docker-compose.yml

@@ -11,10 +11,13 @@ services:
        - db_data:/var/lib/mysql
      restart: always
      environment:
-       MYSQL_ROOT_PASSWORD: somewordpress
+       MYSQL_ROOT_PASSWORD_FILE: /run/secrets/db_root_password
        MYSQL_DATABASE: wordpress
        MYSQL_USER: wordpress
-       MYSQL_PASSWORD: wordpress
+       MYSQL_PASSWORD_FILE: /run/secrets/db_password
+     secrets:
+       - db_root_password
+       - db_password
 
    wordpress:
      depends_on:
@@ -26,6 +29,14 @@ services:
      environment:
        WORDPRESS_DB_HOST: db:3306
        WORDPRESS_DB_USER: wordpress
-       WORDPRESS_DB_PASSWORD: wordpress
+       WORDPRESS_DB_PASSWORD_FILE: /run/secrets/db_password
+     secrets:
+       - db_password
 volumes:
   db_data:
+
+secrets:
+  db_root_password:
+    file: ./secrets/db_root_password.txt
+  db_password:
+    file: ./secrets/db_password.txt