Part 1: Docker networking domain sharing

Take a look at this test yaml file.

ubuntu@ip-172-31-11-243:~$ cat alipapa.yml
version: "3.5"
services:
  ali01:
    image: ubuntu:16.04
    hostname: ali01
    container_name: ali01
    domainname: papa.com
    networks:
      papa.com:
        aliases:
          - ali01.papa.com
    entrypoint: sleep infinity
  ali02:
    image: ubuntu:16.04
    hostname: ali02
    container_name: ali02
    domainname: papa.com
    networks:
      papa.com:
        aliases:
          - ali02.papa.com
    entrypoint: sleep infinity
networks:
  papa.com:
    driver: bridge

When you are bringing up all these containers, considering that you tap into ali01 and ping ali02, what is your expected result.

ubuntu@ip-172-31-11-243:~$ docker-compose -f alipapa.yml up -d
Creating network "ubuntu_papa.com" with driver "bridge"
Creating ali02 ... done
Creating ali01 ... done
ubuntu@ip-172-31-11-243:~$ docker ps -a
CONTAINER ID        IMAGE                  COMMAND                  CREATED             STATUS                       PORTS               NAMES
fdbfb1a48686        ubuntu:16.04           "sleep infinity"         7 seconds ago       Up 6 seconds                                     ali02
7566e8c7db8b        ubuntu:16.04           "sleep infinity"         7 seconds ago       Up 5 seconds                                     ali01

ubuntu@ip-172-31-11-243:~$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
07cb97e27689        bridge              bridge              local
e81946364c3d        host                host                local
b285c6c7236e        none                null                local
5fb1bdc9f13e        ubuntu_papa.com     bridge              local

Wait... I didn't actually creating ubuntu_papa.com domain? Why it is so? Should it be just papa.com?

root@ali01:/# ping ali02
PING ali02 (172.20.0.3) 56(84) bytes of data.
64 bytes from ali02.ubuntu_papa.com (172.20.0.3): icmp_seq=1 ttl=64 time=0.087 ms
64 bytes from ali02.ubuntu_papa.com (172.20.0.3): icmp_seq=2 ttl=64 time=0.053 ms
64 bytes from ali02.ubuntu_papa.com (172.20.0.3): icmp_seq=3 ttl=64 time=0.062 ms

root@ali01:/# ping ali02.papa.com
PING ali02.baba.com (172.20.0.3) 56(84) bytes of data.
64 bytes from ali02.ubuntu_papa.com (172.20.0.3): icmp_seq=1 ttl=64 time=0.063 ms
64 bytes from ali02.ubuntu_papa.com (172.20.0.3): icmp_seq=2 ttl=64 time=0.061 ms
64 bytes from ali02.ubuntu_papa.com (172.20.0.3): icmp_seq=3 ttl=64 time=0.065 ms

Scratching head moment. 😓😓😓