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