Docker DNS

.DockerDNS.md

Build

docker build --rm -t dns PATH_TO_DOCKERFILE
chmod +x dns.sh
mkdir -p /opt/docker && sudo mv dns.sh /opt/docker/dns

Run

Each time you change your dns

/opt/docker/run

dns.sh

#!/usr/bin/env python

import subprocess
import socket
import fcntl
import struct
import sys
import os

if os.geteuid() != 0:
    os.execvp("sudo", ["sudo"] + sys.argv)


def get_ip_address(ifname):
    ''' retreive IP from given interface name
    '''
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    return socket.inet_ntoa(fcntl.ioctl(
        s.fileno(),
        0x8915,    # SIOCGIFADDR
        struct.pack('256s', ifname[:15])
    )[20:24])

get_ip_address('eth0')    # '192.168.0.110'

# Retreive Docker0 IP
docker_ip = get_ip_address('docker0')
if not docker_ip:
    print('\033[31mNo IP found for interface docker\033[0m')
    sys.exit(1)

print('Docker0 IP %s' % docker_ip)

# Restore previous resolv
with open('/etc/resolvconf/resolv.conf.d/head', 'r') as f:
    resolvconf = [x.strip() for x in f if '# docker-dns' not in x]
with open('/etc/resolvconf/resolv.conf.d/head', 'w') as f:
    f.write('\n'.join(resolvconf) + '\n')
subprocess.call(['resolvconf', '-u'])

# Get default DNS
(resolv, _) = subprocess.Popen(['docker', 'run', '--rm', 'busybox', 'cat', '/etc/resolv.conf'], stdout=subprocess.PIPE).communicate()
dns_servers = [x for x in [x[11:].strip() for x in resolv.splitlines() if x.startswith('nameserver ')] if x not in ('127.0.0.1', docker_ip)]
if not len(dns_servers):
    print('\033[31mNo name server found. Dis you use 127.0.0.1?\033[0m')
    sys.exit(1)

# Remove previous dns container
subprocess.Popen(['docker', 'rm', '-f', 'dns'], stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()

# Start dns container
subprocess.call(['docker', 'run', '-td', '--name', 'dns', '-p', '%s:53:53/udp' % docker_ip, '-v', '/var/run/docker.sock:/var/run/docker.sock', 'cc-dns'])

# Add container in resolvconf
resolvconf.append('nameserver %s # docker-dns' % docker_ip)
with open('/etc/resolvconf/resolv.conf.d/head', 'w') as f:
    f.write('\n'.join(resolvconf) + '\n')
subprocess.call(['resolvconf', '-u'])

dnsmasq.tmpl

{{ range $host, $containers := groupByMulti $ "Env.DOMAIN_NAME" "," }}
{{ range $index, $container := $containers }}
{{ with $address := index $container.Addresses 0 }}
address=/{{ $host }}/{{ $address.IP }}
{{ end }}
{{ end }}
{{ end }}

Dockerfile

FROM debian:latest

RUN apt-get update \
 && apt-get install --no-install-recommends -y \
    dnsmasq \
    supervisor \

 && apt-get clean \
 && rm -r /var/lib/apt/lists/*

ENV DOCKER_GEN_VERSION 0.3.6

RUN apt-get update \
 && apt-get install  --no-install-recommends -y \
    wget \

 && wget --no-check-certificate -qO- https://github.com/jwilder/docker-gen/releases/download/$DOCKER_GEN_VERSION/docker-gen-linux-amd64-$DOCKER_GEN_VERSION.tar.gz | tar xvz -C /usr/local/bin \

 && apt-get purge -y wget \

 && apt-get clean \
 && rm -r /var/lib/apt/lists/*

ENV DOCKER_HOST unix:///var/run/docker.sock

ADD dnsmasq.tmpl /etc/dnsmasq.tmpl
ADD supervisord.conf /etc/supervisor/conf.d/docker-gen.conf

EXPOSE 53/udp

CMD ["/usr/bin/supervisord", "-n"]

supervisord.conf

[program:docker-gen]
command=docker-gen -watch -only-exposed -notify "supervisorctl restart dnsmasq" /etc/dnsmasq.tmpl /etc/dnsmasq.conf
redirect_stderr=true
priority=1

[program:dnsmasq]
command=dnsmasq -d -k
redirect_stderr=true