wait for DNS

wait_for_dns.py

#!/usr/bin/env python

try:
    import dns.exception
    import dns.resolver
except ImportError as ex:
    raise SystemExit('You need to pip install dnspython')
import signal
import sys


timeout_seconds = 300

class TimeoutError(BaseException):
    pass

def handler(signum, frame):
    raise TimeoutError('{}\n{}'.format(signum, frame))

signal.signal(signal.SIGALRM, handler)
signal.alarm(timeout_seconds)

dns_ex = None

if __name__ == '__main__':
    fqdn = sys.argv[1]
    print 'Waiting up to {0} seconds for {1}'.format(timeout_seconds, fqdn)

    while True:
        try:
            ans = dns.resolver.query(fqdn)
            break
        except dns.resolver.NXDOMAIN as ex:
            pass
        except TimeoutError as ex:
            raise SystemExit('Timed out waiting for DNS')

    signal.alarm(0)
    print 'DNS: {}'.format(ans.rrset)