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, domains, database=None):
  20         common.ResolverBase.__init__(self)
  21         if database is not None:
  22             sipb_xen_database.connect(database)
  23         self.domains = domains
  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 name.lower() in self.domains:
  44             domain = name.lower()
  45         else:
  46             for domain in self.domains:
  47                 if name.lower().endswith('.'+domain):
  48                     break
  49             else: #Not us
  50                 return defer.fail(failure.Failure(dns.DomainError(name)))
  51         results = []
  52         if cls == dns.IN and type in (dns.A, dns.ALL_RECORDS):
  53             host = name[:-len(domain)-1]
  54             if not host:
  55                 ttl = 900
  56                 record = dns.Record_CNAME('sipb-xen-dev.mit.edu', ttl)
  57                 results.append(dns.RRHeader(name, dns.CNAME, dns.IN,
  58                                             ttl, record, auth=True))
  59             else:
  60                 value = sipb_xen_database.Machine.get_by(name=host)
  61                 if value is None or not value.nics:
  62                     return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  63                 ip = value.nics[0].ip
  64                 if ip is None:  #Deactivated?
  65                     return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  66                 ttl = 900
  67                 record = dns.Record_A(ip, ttl)
  68                 results.append(dns.RRHeader(name, dns.A, dns.IN,
  69                                             ttl, record, auth=True))
  70         authority = []
  71         authority.append(dns.RRHeader(domain, dns.SOA, dns.IN, 3600,
  72                                       self.soa, auth=True))
  73         return defer.succeed((results, authority, []))
  74         #Doesn't exist
  75         return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  76
  77 if '__main__' == __name__:
  78     resolver = DatabaseAuthority(['servers.csail.mit.edu',
  79                                   'xvm.mit.edu'],
  80                                  'postgres://sipb-xen@sipb-xen-dev/sipb_xen')
  81
  82     verbosity = 0
  83     f = server.DNSServerFactory(authorities=[resolver], verbose=verbosity)
  84     p = dns.DNSDatagramProtocol(f)
  85     f.noisy = p.noisy = verbosity
  86
  87     reactor.listenUDP(53, p)
  88     reactor.listenTCP(53, f)
  89     reactor.run()