DNS Python Script to Modify Zone File(s) getting relativity error and inserting escape characters

Question

Relatively new to python and programming in general but would like to automate a DNS migration I'm working on for a large # of domains.

Shamelessly stole some initial framework from AgileTesting Blog.

In it's current state the script

• fails to save with errors
• inserts escape characters in the new name server records

I can remark out the rdata.rname = respname in the soarr(respname) function so I know it's something specific there. Not sure how to drill down into the issue based on the error.

For the escape characters, I feel like it's something simple but my brain is mushy so just including it as a minor problem.

#!/bin/python3
import re,sys
import dns.zone
from dns.exception import DNSException
from dns.rdataclass import *
from dns.rdatatype import *

script, filename, nameservers = sys.argv
sourcefile = open(filename,"r")

def soarr(respname):
        for (name, ttl, rdata) in zone.iterate_rdatas(SOA):
                serial = rdata.serial
                old_name = rdata.rname
                new_serial = serial + 1
                print ("Changing SOA serial from %d to %d" %(serial, new_serial))
                print ("Changing responsible name from %s to %s" %(old_name, respname))
                rdata.serial = new_serial
                rdata.rname = respname
                rdata.expire = 3600
                print (rdata.rname)

def nsrr(nameserver):
        NS_add = "@"
        target = dns.name.Name((nameserver,))
        print ("Adding record of type NS:", NS_add)
        rdataset = zone.find_rdataset(NS_add, rdtype=NS, create=True)
        rdata = dns.rdtypes.ANY.NS.NS(IN, NS, target)
        rdataset.add(rdata, ttl=3600)
        print (rdata)

def savefile(domain):
        print ("debug",domain)
        new_zone_file = "new.%s.hosts" % domain
        print ("Writing modified zone to file %s" % new_zone_file)
        zone.to_file(new_zone_file,domain)

for domainitem in sourcefile:
        domainitem = domainitem.rstrip()
        print ("Processing %s." % domainitem)
        zone_file = '%s.hosts' % domainitem
        zone = dns.zone.from_file(zone_file, domainitem)

# Updating the SOA record, responsible name, lowering TTL and incrementing serial of the zone file.
        soarr('systems.example.com')

# Adding name servers to the zone file.
        if nameservers == 'customer':
                nsrr('ns01.example.com')
        if nameservers == 'core':
                nsrr("ns01.example2.com")
        if nameservers == 'internal':
                nsrr("ns01.int.example2.com")

# Save the file as a new file.
        savefile(domainitem)

The intent is to cycle through a list of domains from a file, open the appropriate zone file, manipulate the zone and save the changes to a newly named file.

Error on save failure.

Traceback (most recent call last):
  File "./zonefile.py", line 62, in <module>
    savefile(domainitem)
  File "./zonefile.py", line 36, in savefile
    zone.to_file(new_zone_file,domain)
  File "/usr/local/lib/python3.6/site-packages/dns/zone.py", line 531, in to_file
    relativize=relativize)
  File "/usr/local/lib/python3.6/site-packages/dns/node.py", line 51, in to_text
    s.write(rds.to_text(name, **kw))
  File "/usr/local/lib/python3.6/site-packages/dns/rdataset.py", line 218, in to_text
    **kw)))
  File "/usr/local/lib/python3.6/site-packages/dns/rdtypes/ANY/SOA.py", line 62, in to_text
    rname = self.rname.choose_relativity(origin, relativize)
AttributeError: 'str' object has no attribute 'choose_relativity'

As mentioned, remarking out the single line let's the file save. In the saved file the NS entries show escape characters.

@ 3600 IN NS ns01\.example\.com

Answer 1

Both of the issues you've encountered - the AttributeError and the escape characters - are because you're not creating your dns.name.Names correctly.

To create a dns.name.Name from a str, it's best to call dns.name.from_text().

Example: name = dns.name.from_text('example.com')

Specifically, in your nsrr function, the second line should be changed to

target = dns.name.from_text(nameserver)

And in your soarr function, you fix it with:

rdata.rname = dns.name.from_text(respname)

Here's a copy of the changes I made (also some minor indentation changes as well).

#!/bin/python3
import re
import sys
import dns.zone
from dns.exception import DNSException
from dns.rdataclass import *
from dns.rdatatype import *

script, filename, nameservers = sys.argv
sourcefile = open(filename,"r")

def soarr(respname):
    for (name, ttl, rdata) in zone.iterate_rdatas(SOA):
        serial = rdata.serial
        old_name = rdata.rname
        new_serial = serial + 1
        print ("Changing SOA serial from %d to %d" %(serial, new_serial))
        print ("Changing responsible name from %s to %s" %(old_name, respname))
        rdata.serial = new_serial
        rdata.rname = respname
        rdata.expire = 3600
        print (rdata.rname)

def nsrr(nameserver):
    NS_add = "@"
    target = dns.name.from_text(nameserver)
    print ("Adding record of type NS:", NS_add)
    rdataset = zone.find_rdataset(NS_add, rdtype=NS, create=True)
    rdata = dns.rdtypes.ANY.NS.NS(IN, NS, target)
    rdataset.add(rdata, ttl=3600)
    print (rdata)

def savefile(domain):
    print ("debug",domain)
    new_zone_file = "new.%s.hosts" % domain
    print ("Writing modified zone to file %s" % new_zone_file)
    zone.to_file(new_zone_file,domain)

for domainitem in sourcefile:
    domainitem = domainitem.rstrip()
    print ("Processing %s." % domainitem)
    zone_file = '%s.hosts' % domainitem
    zone = dns.zone.from_file(zone_file, domainitem)

    # Updating the SOA record, responsible name, lowering TTL and incrementing serial of the zone file.
    soarr(dns.name.from_text('systems.example.com'))

    # Adding name servers to the zone file.
    if nameservers == 'customer':
        nsrr('ns01.example.com')
    if nameservers == 'core':
        nsrr("ns01.example2.com")
    if nameservers == 'internal':
        nsrr("ns01.int.example2.com")

    # Save the file as a new file.
    savefile(domainitem)