code/dnsserver.py

   1 #!/usr/bin/python
   2 from twisted.internet import reactor
   3 from twisted.names import server
   4 from twisted.names import dns
   5 from twisted.names import common
   6 from twisted.internet import defer
   7 from twisted.python import failure
   8
   9 import sipb_xen_database
  10 import psycopg2
  11 import sqlalchemy
  12 import time
  13
  14 class DatabaseAuthority(common.ResolverBase):
  15     """An Authority that is loaded from a file."""
  16
  17     soa = None
  18
  19     def __init__(self, domain, database=None):
  20         common.ResolverBase.__init__(self)
  21         if database is not None:
  22             sipb_xen_database.connect(database)
  23         self.domain = domain
  24         self.soa = dns.Record_SOA(mname='sipb-xen-dev.mit.edu',
  25                                   rname='sipb-xen.mit.edu',
  26                                   serial=1, refresh=3600, retry=900,
  27                                   expire=3600000, minimum=21600, ttl=3600)
  28     def _lookup(self, name, cls, type, timeout = None):
  29         for i in range(3):
  30             try:
  31                 value = self._lookup_unsafe(name, cls, type, timeout = None)
  32             except (psycopg2.OperationalError, sqlalchemy.exceptions.SQLError):
  33                 if i == 2:
  34                     raise
  35                 print "Reloading database"
  36                 time.sleep(0.5)
  37                 continue
  38             else:
  39                 return value
  40
  41     def _lookup_unsafe(self, name, cls, type, timeout):
  42         sipb_xen_database.clear_cache()
  43         if not (name.lower() == self.domain or
  44                 name.lower().endswith('.'+self.domain)):
  45             #Not us
  46             return defer.fail(failure.Failure(dns.DomainError(name)))
  47         results = []
  48         if cls == dns.IN and type in (dns.A, dns.ALL_RECORDS):
  49             host = name[:-len(self.domain)-1]
  50             value = sipb_xen_database.Machine.get_by(name=host)
  51             if value is None or not value.nics:
  52                 return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  53             ip = value.nics[0].ip
  54             if ip is None:  #Deactivated?
  55                 return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  56             ttl = 900
  57             record = dns.Record_A(ip, ttl)
  58             results.append(dns.RRHeader(name, dns.A, dns.IN,
  59                                         ttl, record, auth=True))
  60         authority = []
  61         authority.append(dns.RRHeader(self.domain, dns.SOA, dns.IN, 3600,
  62                                       self.soa, auth=True))
  63         return defer.succeed((results, authority, []))
  64         #Doesn't exist
  65         return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  66
  67 if '__main__' == __name__:
  68     resolver = DatabaseAuthority('servers.csail.mit.edu',
  69                                  'postgres://sipb-xen@sipb-xen-dev/sipb_xen')
  70
  71     verbosity = 0
  72     f = server.DNSServerFactory(authorities=[resolver], verbose=verbosity)
  73     p = dns.DNSDatagramProtocol(f)
  74     f.noisy = p.noisy = verbosity
  75
  76     reactor.listenUDP(53, p)
  77     reactor.listenTCP(53, f)
  78     reactor.run()