nginx-proxy backend wordpress compose file

wordpress-compose.yml

version: "3"

services:
   db_node_domain_a:
     image: mysql:5.7
     volumes:
       - db_data_mysql_a:/var/lib/mysql
     restart: always
     ports:
        - $PORTS_A:3306
     environment:
       MYSQL_ROOT_PASSWORD: $MYSQL_ROOT_PASSWORD
       MYSQL_DATABASE: $MYSQL_DATABASE
       MYSQL_USER: $MYSQL_USER
       MYSQL_PASSWORD: $MYSQL_PASSWORD
     container_name: wordpress_db_a

   wordpress_a:
     depends_on:
       - db_node_domain_a
     image: wordpress:latest
     expose:
       - 80
     restart: always
     environment:
       VIRTUAL_HOST: $V_HOST_A
       LETSENCRYPT_HOST: $V_HOST_A
       LETSENCRYPT_EMAIL: $EMAIL
       WORDPRESS_DB_HOST: db_node_domain_a:3306
       WORDPRESS_DB_USER: $MYSQL_USER
       WORDPRESS_DB_PASSWORD: $MYSQL_PASSWORD
     container_name: wordpress_a
  
  # another wordpress   
   db_node_domain_b:
     image: mysql:5.7
     volumes:
       - db_data_mysql_b:/var/lib/mysql
     restart: always
     ports:
        - $PORTS_B:3306
     environment:
       MYSQL_ROOT_PASSWORD: $MYSQL_ROOT_PASSWORD
       MYSQL_DATABASE: $MYSQL_DATABASE
       MYSQL_USER: $MYSQL_USER
       MYSQL_PASSWORD: $MYSQL_PASSWORD
     container_name: wordpress_db_b

   wordpress_b:
     depends_on:
       - db_node_domain_b
     image: wordpress:latest
     expose:
       - 80
     restart: always
     environment:
       VIRTUAL_HOST: $V_HOST_B
       LETSENCRYPT_HOST: $V_HOST_B 
       LETSENCRYPT_EMAIL: $EMAIL
       WORDPRESS_DB_HOST: db_node_domain_b:3306
       WORDPRESS_DB_USER: $MYSQL_USER
       WORDPRESS_DB_PASSWORD: $MYSQL_PASSWORD
     container_name: wordpress_b     
     
volumes:
    db_data_mysql_a:
    db_data_mysql_b:

networks:
  default:
    external:
      name: nginx-proxy