fast DNS resolution

fast_resolv.py

#!/usr/bin/env python
import json
import dns.resolver
import multiprocessing as mp

def worker(hostname, results):
    resolv = dns.resolver.Resolver()
    resolv.nameservers = [
        '8.8.8.8', # Google
        '8.8.4.4', # Google
        '9.9.9.9', # Quad9
        '149.112.112.112', # Quad9
        '208.67.222.222', # openDNS
        '208.67.220.220', # openDNS
        '1.1.1.1', # cloudflare
        '1.0.0.1', # cloudflare
        '64.6.64.6', # verisign
        '64.6.65.6', # verisign
    ]
    records = {
        'A': [],
        'MX': [],
        'NS': []
    }
    for rtype in ['A', 'MX', 'NS']:
        try:
            output = resolv.query(hostname, rtype)
            for _ in output:
                if _ not in records[rtype]:
                    records[rtype].append(str(_))
            print('found {} answers for {} IN {}'.format(len(records[rtype]), hostname, rtype))
            results.append({hostname: records})
        except Exception as e:
            print('{} did not answer to {}'.format(hostname))
            open('./failed_resolv.txt', 'a+').write('{}\n'.format(hostname))

def main():
    hostnames = open('./hostnames.txt', 'r').read().splitlines()

    # Send jobs to multiprocessing pool
    manager = mp.Manager()
    results = manager.list() # results list
    pool = mp.Pool(16)
    jobs = []

    for hostname in hostnames:
        pool.apply_async(worker, args=(hostname, results,))
    # close the pool as processing is complete
    pool.close()
    pool.join()

    # Write output
    json.dump(list(results), open('./resolv.json', 'w+'))

if __name__ == '__main__':
    main()