Communicating between Docker containers in different networks on the same host

In this guide, I will explain how to connect two containers in different docker-compose.yml Services together that are setup on the same host machine.

By default every docker-compose.yml Service is generating its own bridge-Network so that containers inside can communicate between each other.

But communications between two docker-compose.yml Services on the same host machine are blocked by docker. So we need to create a new "custom" bridge-Network if two containes in different docker-cmpose.yml Services need to communicate between each other.

In this example I want to connect web-app1 container with the DB2 container from different docker-compose.yml Services.

More information about this topic can be found on the offical docker documentation: https://docs.docker.com/compose/networking

1. We need to create the custom bridge-Network:

   For the custom bridge-Network you can use your own name. In my example I chose the name serv1_link_serv2

   sudo docker network create -d bridge serv1_link_serv2

2. Now create the two docker-compose.yml files and connect web-app1- and db2-container together over the serv1_link_serv2 bridge-Network.

   docker-compose1.yml

   version: "3"
   services:
    db1:
      image: "mariadb:latest"
      ........
   
    web-app1:
      image: "php:apache"
      ........
      networks:
        - serv1_link_serv2
        - default
   
   networks:
    serv1_link_serv2
      name: serv1_link_serv2
      external: true

   docker-compose2.yml

   version: "3"
   services:
    db2:
      image: "mariadb:latest"
      ........
      networks:
        - serv1_link_serv2
        - default
   
    web-app2:
      image: "php:apache"
      ........
   
   networks:
    serv1_link_serv2
      name: serv1_link_serv2
      external: true