Join an existing network from a docker container in docker compose

In some scenarios, we might need to connect to an existing network from a docker container instead of create a new network. This would let us allow the resources in the existing network.

To join an existing network, you can define a network under each service and at the end of the docker compose file you can define the network to use the existing external network.

Syntax

services:
  service_name:
    image: image_name:latest
    restart: always
    networks:
      - existing-network
networks:
  existing-network:
    external: true