Same named network for multiple docker compose files

README.md

Same Network for Multiple docker-compose files

The A file creates the network. The B file connects to it.

Run

docker-compose -f docker-compose-A.yaml up -d
docker-compose -f docker-compose-B.yaml up -d

Testing what names Docker puts into DNS:

docker exec -it test_a ash

Then inside the container:

/ # apk add bind-tools
...
/ # echo test_a_service test_a a test_b_service test_b b blah | xargs -n 1 host
test_a_service has address 172.20.0.2
test_a has address 172.20.0.2
a has address 172.20.0.2
test_b_service has address 172.20.0.3
test_b has address 172.20.0.3
b has address 172.20.0.3
Host blah not found: 3(NXDOMAIN)

docker-compose-A.yaml

version: '3.5'
services:
  # All 3 names will resolve in DNS:
  #   - test_a_service
  #   - test_a
  #   - a
  test_a_service:
    container_name: test_a
    image: python:3.6-alpine3.7
    command: sleep 10000
    restart: always
    networks:
      name_only_for_file:
        aliases:
          - a


networks:
  name_only_for_file:
    name: test_net

docker-compose-B.yaml

version: '3.5'
services:
  # All 3 names will resolve in DNS:
  #   - test_b_service
  #   - test_b
  #   - b
  test_b_service:
    container_name: test_b
    image: python:3.6-alpine3.7
    command: sleep 10000
    restart: always
    networks:
      another_name_only_for_file:
        aliases:
          - b

networks:
  another_name_only_for_file:
    external:
      name: test_net