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         self.ns = dns.Record_NS(name='ns1.xvm.mit.edu', ttl=3600)
  29         record = dns.Record_A(address='18.181.0.62', ttl=3600)
  30         self.ns1 = dns.RRHeader('ns1.xvm.mit.edu', dns.A, dns.IN,
  31                                 3600, record, auth=True)
  32
  33
  34     def _lookup(self, name, cls, type, timeout = None):
  35         for i in range(3):
  36             try:
  37                 value = self._lookup_unsafe(name, cls, type, timeout = None)
  38             except (psycopg2.OperationalError, sqlalchemy.exceptions.SQLError):
  39                 if i == 2:
  40                     raise
  41                 print "Reloading database"
  42                 time.sleep(0.5)
  43                 continue
  44             else:
  45                 return value
  46
  47     def _lookup_unsafe(self, name, cls, type, timeout):
  48         sipb_xen_database.clear_cache()
  49
  50         ttl = 900
  51         name = name.lower()
  52         if name in self.domains:
  53             domain = name
  54         else:
  55             # This works because domain will remain bound after breaking out of the loop
  56             for domain in self.domains:
  57                 if name.endswith('.'+domain):
  58                     break
  59             else: #Not us
  60                 return defer.fail(failure.Failure(dns.DomainError(name)))
  61         results = []
  62         authority = []
  63         additional = [self.ns1]
  64         authority.append(dns.RRHeader(domain, dns.NS, dns.IN,
  65                                       3600, self.ns, auth=True))
  66         if cls == dns.IN:
  67             if type in (dns.A, dns.ALL_RECORDS):
  68                 host = name[:-len(domain)-1]
  69                 if not host:
  70                     record = dns.Record_A('18.181.0.62', ttl)
  71                     results.append(dns.RRHeader(name, dns.A, dns.IN,
  72                                                 ttl, record, auth=True))
  73                 else:
  74                     value = sipb_xen_database.Machine.get_by(name=host)
  75                     if value is None or not value.nics:
  76                         return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  77                     ip = value.nics[0].ip
  78                     if ip is None:  #Deactivated?
  79                         return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  80                     record = dns.Record_A(ip, ttl)
  81                     results.append(dns.RRHeader(name, dns.A, dns.IN,
  82                                                 ttl, record, auth=True))
  83             elif type == dns.NS:
  84                 results.append(dns.RRHeader(domain, dns.NS, dns.IN,
  85                                             ttl, self.ns, auth=True))
  86                 authority = []
  87             elif type == dns.SOA:
  88                 results.append(dns.RRHeader(domain, dns.SOA, dns.IN,
  89                                             ttl, self.soa, auth=True))
  90             return defer.succeed((results, authority, additional))
  91         else:
  92             #Doesn't exist
  93             return defer.fail(failure.Failure(dns.AuthoritativeDomainError(name)))
  94
  95 if '__main__' == __name__:
  96     resolver = DatabaseAuthority(['servers.csail.mit.edu',
  97                                   'xvm.mit.edu'],
  98                                  'postgres://sipb-xen@sipb-xen-dev/sipb_xen')
  99
 100     verbosity = 0
 101     f = server.DNSServerFactory(authorities=[resolver], verbose=verbosity)
 102     p = dns.DNSDatagramProtocol(f)
 103     f.noisy = p.noisy = verbosity
 104
 105     reactor.listenUDP(53, p)
 106     reactor.listenTCP(53, f)
 107     reactor.run()