docker-machine DNS server

This package fires up a tiny (~100 lines) DNS server whose sole purpose is to listen for *.docker DNS lookups and resolve the hostname using docker-machine ip.

How it works:

• DNS query for dev.docker comes in
• Server parses out "dev.docker"
• Server responds with the result of $(docker-machine ip dev)

Environment variables

DOCKER_MACHINE_DNS_RESOLVER

Change the default IP resolver from docker-machine ip to your own custom command by setting this environment variable.

DOCKER_MACHINE_DNS_TLD

Change the default tld from docker by setting this environment variable.

Setup:

Install in the usual way:

npm install -g docker-machine-dns

Setup: The easy way

Run this:

sudo mkdir -p /etc/resolver
sudo touch /etc/resolver/docker
sudo chown -R $USER /etc/resolver		

This creates the /etc/resolver directory (if it doesn't already exist) and grants ownership to your current user account. The service will automatically configure the resolver/docker file on each run, making it "just work".

Setup: The way that doesn't require changing ownership of /etc/resolver

Write this to /etc/resolver/docker and always run with the same specified port

nameserver	127.0.0.1
port	12345
search_order	300000
timeout	1

Note: the whitespace separators in this file NEED to be tabs. Spaces won't work.

Example:

$ docker-machine ls
NAME   ACTIVE   DRIVER       STATE     URL                         SWARM
dev             virtualbox   Running   tcp://192.168.99.100:2376
dev2            virtualbox   Running   tcp://192.168.99.101:2376
dev3            virtualbox   Stopped

$ ping -t 4 dev.docker
ping: cannot resolve dev.docker: Unknown host

$ docker-machine-dns &
[1] 18007
Listening on UDP port 55451

$ ping -t 4 dev.docker
PING dev.docker (192.168.99.100): 56 data bytes
64 bytes from 192.168.99.100: icmp_seq=0 ttl=64 time=0.268 ms
64 bytes from 192.168.99.100: icmp_seq=1 ttl=64 time=0.272 ms
64 bytes from 192.168.99.100: icmp_seq=2 ttl=64 time=0.313 ms
64 bytes from 192.168.99.100: icmp_seq=3 ttl=64 time=0.454 ms

--- dev.docker ping statistics ---
4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.268/0.327/0.454/0.076 ms

$ ping -t 4 dev2.docker
PING dev2.docker (192.168.99.101): 56 data bytes
64 bytes from 192.168.99.101: icmp_seq=0 ttl=64 time=0.232 ms
64 bytes from 192.168.99.101: icmp_seq=1 ttl=64 time=0.394 ms
64 bytes from 192.168.99.101: icmp_seq=2 ttl=64 time=0.284 ms
64 bytes from 192.168.99.101: icmp_seq=3 ttl=64 time=0.222 ms

--- dev2.docker ping statistics ---
4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.222/0.283/0.394/0.068 ms

docker-machine-dns can take a UDP port as its first (and only) argument to bind to that specific port instead of randomly picking one on each run.