Solve host machine IP from anywhere

Just use host.docker

$ ping host.docker
PING host.docker (172.21.0.1) 56(84) bytes of data.
64 bytes from 172.21.0.1 (172.21.0.1): icmp_seq=1 ttl=64 time=0.086 ms
64 bytes from 172.21.0.1 (172.21.0.1): icmp_seq=2 ttl=64 time=0.076 ms
64 bytes from 172.21.0.1 (172.21.0.1): icmp_seq=3 ttl=64 time=0.081 ms

You can customize this hostname by setting

Environment variable

$ docker run dns-proxy-server -e MG_HOST_MACHINE_HOSTNAME=$(cat /etc/hostname)

Command line option

$ ./dns-proxy-server --host-machine-hostname $(cat /etc/hostname)

Json configuration

{
	"hostMachineHostname": "host.docker" 
}

Notes:

Be aware if you set the host machine hostname as the machine name then you will have to remove its name from /etc/hosts since OS try to resolve names from hosts file first then from DNS server