Docker - Adding new Wordpress container to existing SQL database container - docker

Question

I'm trying to understand or find information on how I would connect a new Wordpress container to an existing MariaDB container. I'm missing something. I can add a Wordpress instance while also creating the MariaDB container. See below.
services:
wordpress:
image: wordpress
restart: always
ports:
- 8282:80
environment:
WORDPRESS_DB_HOST: db
WORDPRESS_DB_USER: exampleuser
WORDPRESS_DB_PASSWORD: examplepass
WORDPRESS_DB_NAME: exampledb
volumes:
- ./:/var/www/html
links:
- db:db
db:
image: mariadb:latest
restart: always
container_name: mariadb
environment:
MYSQL_DATABASE: exampledb
MYSQL_USER: exampleuser
MYSQL_PASSWORD: examplepass
MYSQL_ROOT_PASSWORD: password
volumes:
- db:/var/lib/mysql
phpmyadmin:
image: phpmyadmin/phpmyadmin
restart: always
container_name: phpmyadmin
ports:
- "8081:80"
environment:
PMA_HOST: mariadb
volumes:
wordpress:
db:
phpmyadmin:```
After that has spun up and is good to go, I then attempt another docker-compose.yml (see below) and I cannot get the Wordpress instance to connect to the SQL instance.
```version: '3.7'
services:
wordpress:
image: wordpress
restart: always
container_name: wordup
ports:
- 8283:80
environment:
WORDPRESS_DB_HOST: 172.20.0.3
WORDPRESS_DB_USER: username
WORDPRESS_DB_PASSWORD: password
WORDPRESS_DB_NAME: wp2
volumes:
- ./:/var/www/html
volumes:
wp2:
How would I point the new WP instance to the database that I created on the MariaDB container? Is it possible to point new Docker Compose stacks to an already created DB without recreating a new DB? I know that it's not a good idea to share DB's across different applications, but I have a need to pull in data from one Wordpress site to another.
Thanks!

Answer 1

You can use Docker networks. You need to connect two docker-compose files to the same network and inside this network containers can reference each other by container name.
Here is more information about docker-compose networking in the documentation: https://docs.docker.com/compose/networking/#specify-custom-networks
Take a look at an example with two Nginx proxies that started using different docker-compose files. The first proxy redirects to the second one and then it redirects us to google.com.
First proxy docker-compose.yml
version: "3.9"
services:
first:
build: .
ports:
- "8081:80"
networks:
- "test-network"
networks:
test-network:
name: "test-network"
driver: "bridge"
First proxy ngnix.conf
events {}
http {
server {
location / {
proxy_pass http://second:80; # in second docker-compose file we're setting container_name to "second", thus we can reference second container by this name
}
}
}
Second proxy docker-compose.yml:
version: "3.9"
services:
second:
container_name: "second" # note, that we don't need to expose ports because we don't need to make this service visible to a host. But it's not restricted to expose ports. You can do so if you need.
build: .
networks:
- "test-network"
networks:
test-network:
name: "test-network"
driver: "bridge"
Second proxy ngnix.conf:
events {}
http {
server {
location / {
proxy_pass https://google.com;
}
}
}