dockerDNS.py

#!/usr/bin/env python3
"""
Resolve docker container's name into IPv4 address

  python3 docker-dns.py
"""


import argparse
import signal
import sys
from dockerDNS import DNS_PORT, LISTEN_ADDRESS, DockerDNS


def getForwarders(forwarders=None, listenAddress=LISTEN_ADDRESS):
    """
    Reads forwarders from arguments or from resolv.conf and create a list of
    tuples containing the forwarders' IP and the port.
    """
    if forwarders is None:
        forwarders = []
        with open("/etc/resolv.conf", "r") as resolvconf:
            for line in resolvconf:
                if line.startswith("nameserver"):
                    if line[11:-1] == listenAddress:
                        continue
                    else:
                        forwarders.append((line[11:-1], DNS_PORT))
            if len(forwarders) == 0:
                forwarders = None
    else:
        forwarders = forwarders.split(",")
        forwarders = [(address, DNS_PORT) for address in forwarders]
    return forwarders


class DNSHandler():
    """Handle DockerDNS start and stop"""
    def __init__(self, port=DNS_PORT,
                 listenAddress=LISTEN_ADDRESS,
                 forwarders=None):
        self.runner = DockerDNS(port=port,
                                listenAddress=listenAddress,
                                forwarders=forwarders)
        signal.signal(signal.SIGTERM, self.signal_handler)
        signal.signal(signal.SIGINT, self.signal_handler)

    def signal_handler(self, signum, frame):
        """Signal handler that can stop the runner"""
        self.runner.stop()

    def start(self):
        """Runner starter"""
        self.runner.start()

    def clean(self):
        """Runner cleaner"""
        self.runner.clean()


if __name__ == "__main__":
    description = "Resolve docker container's name into IPv4 address"
    parser = argparse.ArgumentParser(description=description)
    parser.add_argument("--port",
                        type=int,
                        default=DNS_PORT)
    parser.add_argument("--listen-address",
                        dest="listenAddress",
                        default=LISTEN_ADDRESS)
    parser.add_argument("--forwarders",
                        default=None)
    options = parser.parse_args()
    forwarders = getForwarders(forwarders=options.forwarders,
                               listenAddress=options.listenAddress)

    DNSHandler = DNSHandler(port=options.port,
                            listenAddress=options.listenAddress,
                            forwarders=forwarders)
    DNSHandler.start()
    DNSHandler.clean()

    sys.exit()