bind.conf

options {
    directory "/home/dennis/pdns-bug/inst/var/run/pdns-server/";
};
zone "example.com" IN {
    type master;
    file "example.com.zone";
};

example.com.zone

@  900 SOA  ns0.example.com. domain.example.com.  2016010401 28800 7200 604800 86402
@  900 NS ns0.example.com.
c  900 NS ns0.example.com.
ns0 900 A 127.0.0.1

pdns-backend

#!/usr/bin/python

import logging
import logging.handlers
import os
import platform
import re
import select
import signal
import sys
import syslog

# Non-blocking Syslog logging handler
class SysLogLibHandler(logging.Handler):
    """A logging handler that emits messages to syslog.syslog."""
    priority_map = {
        "DEBUG" :    syslog.LOG_DEBUG,
        "INFO" :     syslog.LOG_INFO,
        "WARNING" :  syslog.LOG_WARNING,
        "ERROR" :    syslog.LOG_ERR,
        "CRITICAL" : syslog.LOG_CRIT,
    }

    def __init__(self, facility):
        try:
            syslog.openlog(os.path.basename(sys.argv[0]),logoption=syslog.LOG_PID | syslog.LOG_NDELAY, facility='daemon')
        except Exception:
            pass
        logging.Handler.__init__(self)

    def emit(self, record):
        syslog.syslog(self.priority_map[record.levelname], self.format(record))

class Daemon(object):
    addresses = {
        'www1.c.example.com': '127.0.0.1',
        'www2.c.example.com': '127.0.0.2',
    }

    def __init__(self):
        # 0 - normal operation
        # 1 - SIGHUP received => restarting
        self.restarting = 0
        self.exiting = False
        self.abi_version = None
        signal.signal(signal.SIGINT, self.handle_sigint)
        signal.signal(signal.SIGTERM, self.handle_sigint)
        signal.signal(signal.SIGIO, self.handle_sigint)
        signal.signal(signal.SIGPIPE, self.handle_sigint)
        self.logger = logging.getLogger()
        if sys.stdout.isatty():
            handler = logging.StreamHandler()
            formatter = logging.Formatter("%(filename)s[%(process)d]: %(message)s")
            handler.setFormatter(formatter)
        else:
            handler = SysLogLibHandler(facility='daemon')
        self.logger.addHandler(handler)
        self.logger.setLevel(logging.INFO)

    def handle_sigint(self, signum, frame):
        self.exiting = True
        self.logger.info("Caught signal %d" % signum)

    def handle_sighup(self, signum, frame):
        if self.restarting == 0:
            self.restarting = 1
            self.logger.info("Caught signal %d" % signum)

    def process_requests(self):
        self.logger.info("Backend ready using %s (%s %s)" % (sys.executable, platform.python_implementation(), platform.python_version()))
        signal.signal(signal.SIGHUP, self.handle_sighup)
        while not self.exiting:
            if self.restarting:
                signal.signal(signal.SIGHUP, signal.SIG_IGN)
                self.logger.info("Restarting backend")
                os.execl(sys.argv[0],*sys.argv)
            try:
                rin, rout, rerr = select.select([sys.stdin], [], [], 5)
            except select.error as e:
                # Ignore EINTR
                if e[0] == 4: continue
                else: raise
            if sys.stdin in rin:
                req = sys.stdin.readline().strip()
                self.logger.info("[IN] " + req.replace('\t', '    ').replace('\n', ' - '))
                ans = self.process_single_request(req)
                if ans:
                    sys.stdout.write(ans + "\n")
                    sys.stdout.flush()
                self.logger.info("[OUT] " + ans.replace('\t', '    ').replace('\n', ' - '))
        self.logger.info("Backend exiting")

    def process_single_request(self, req):
        if req == '':
            self.logger.info("EOF from powerdns")
            self.exiting = True
            return ""

        req = req.split('\t')
        reqtype = req[0].lower()
        req = req[1:]
        return getattr(self, 'handle_' + reqtype)(*req)

    def handle_helo(self, abi_version):
        self.abi_version = int(abi_version)
        self.logger.info("Powerdns says hi, API version %d" % self.abi_version)
        if self.abi_version not in (1,2):
            return "FAIL"
        return "OK\tbooking powerdns backend started"

    def handle_axfr(self, id):
        return "FAIL"

    def handle_ping(self):
        return "END"

    def handle_q(self, qname, qclass, qtype, id, remote_ip, local_ip=None):
        if qclass != 'IN' or remote_ip == '0.0.0.0':
            return "END"

        qname_l = qname.lower()
        ret = []

        if qtype == 'ANY':
            self.handle_soa(qname, ret)
            self.handle_ns(qname, ret)
            self.handle_a(qname, ret)
        elif hasattr(self, 'handle_' + qtype.lower()):
            getattr(self, 'handle_' + qtype.lower())(qname, ret)
        else:
            self.logger.error("Cannot handle %s queries" % qtype)
        return "\n".join(ret + ['END'])

    def handle_soa(self, qname, ret):
        if qname.lower() == 'c.example.com':
            soa = "ns0.example.com. postmaster.example.com. 2013112600 14400 900 3628800 300"
            ret.append("DATA\t%s\tIN\tSOA\t%d\t-1\t%s" % (qname, 300,  soa))

    def handle_ns(self, qname, ret):
        if qname.lower() == 'c.example.com':
            for i in range(4):
                ret.append("DATA\t%s\tIN\tNS\t%d\t-1\tns%d.example.com." % (qname, 900,  i))

    def handle_txt(self, qname, ret):
        pass

    def handle_srv(self, qname, ret):
        pass

    def handle_a(self, qname, ret):
        if qname in self.addresses:
            ret.append("DATA\t%s\tIN\tA\t600\t-1\t%s" % (qname, self.addresses[qname]))

if __name__ == '__main__':
    daemon = Daemon()
    try:
        daemon.process_requests()
    except Exception:
        daemon.logger.exception("Exception occured, exiting")

pdns.conf

module-dir=/home/dennis/pdns-bug/inst/lib/pdns
socket-dir=/home/dennis/pdns-bug/inst/var/run/pdns-server
setuid=dennis
setgid=dennis

launch=pipe,bind
version-string=You might very well think I am that version but I could not possibly comment

local-address=127.0.0.1

default-soa-name=domain.example.com

pipebackend-abi-version=2
pipe-command=/home/dennis/pdns-bug/pdns-backend
pipe-timeout=2000
pipe-regex=^([^.]+\.)?c\.example\.com;.*$

# Disable caches
query-cache-ttl=0
cache-ttl=0

# logging
loglevel=7
log-dns-details=no

bind-config=/home/dennis/pdns-bug/bind.conf