Re: [PATCH 1/3] unbound-dhcp-leases-bridge : fix bug 12694 - DHCP hosts not reliably propagated to DNS

Hello,

This is indeed an absolute nightmare what I built here.

It has some advantages over the alternatives of which one is to have the DHCP server execute a couple of commands. The problems there are as follows:

* unbound does not keep a state, so we will have to make sure that we keep the state of all records somewhere and can reload it when the system roboots.

* I have installations with thousands of devices in a single subnet. The DHCP server would just be busy constantly executing any commands which would cause a lot of load. The current Python bridge can use up to 40% of one CPU core at busy times on the same system. I would argue that this approach does not scale well.

* RFC2136 would be great, but we lack too many things to run this properly.

That being said, this is not a great way to solve this problem. I would like to replace some components entirely but probably not soon. The approach that we have works and - apart from the bug - doesn’t suck too hard. Should we do it this way again? No, but we had to try to learn that lesson.

-Michael

On 28 Mar 2022, at 20:32, Jon Murphy jcmurphy26@gmail.com wrote:

Sorry for interrupting this train of thought. Wouldn’t it be easier to use the tools available from dhcpd?

dhcpd seems to have a way execute commands. And I would guess this would be cleaner than "watching" a file.

There are three execute commands: on commit on release on expiry

and these could be used to launch the needed unbound bridge command.

Here is where I found this: https://jpmens.net/2011/07/06/execute-a-script-when-isc-dhcp-hands-out-a-new...

And here is additional info: https://wiki.samba.org/index.php/Configure_DHCP_to_update_DNS_records

(Search for "on commit" on this page)

Jon

...

On Mar 28, 2022, at 12:00 PM, Michael Tremer michael.tremer@ipfire.org wrote:

Hello Anthony,

Thank you very much for submitting this patch and welcome to the list.

I understand that it is easier to track any changes in the directory, but I don’t quite understand why the logic had to be changed that the changes will be applied at the end only.

Is this just to avoid that multiple updates happen one after the other or what are you trying to achieve?

-Michael

...

On 22 Mar 2022, at 03:47, Anthony Heading ajrh@ajrh.net wrote:

Switch from inotify watching individual files to monitoring the containing directories, as because dhcpd renames its leases file into a backup, monitoring the single inode does not work well. Additionally, python appears to have a bug with replacing expired inotify watches on single files.

---

unbound-dhcp-leases-bridge | 47 +++++++++++++++++++++++++------------- 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git unbound-dhcp-leases-bridge unbound-dhcp-leases-bridge index a2df5f1..6e22066 100644 --- unbound-dhcp-leases-bridge +++ unbound-dhcp-leases-bridge @@ -72,6 +72,15 @@ class UnboundDHCPLeasesBridge(object): self.fix_leases_file = fix_leases_file self.hosts_file = hosts_file

• # base mask for a completed file change
  

• mask = inotify.constants.IN_CLOSE_WRITE | inotify.constants.IN_MOVED_TO
  

• # IN_MODIFY since dhcpd appends lease updates to an open file
  

• self.watches = {
  

•     self.leases_file: mask | inotify.constants.IN_MODIFY,
  

•     self.fix_leases_file: mask,
  

•     self.hosts_file: mask
  

• }
  

• self.unbound = UnboundConfigWriter(unbound_leases_file) self.running = False

@@ -80,36 +89,42 @@ class UnboundDHCPLeasesBridge(object): self.running = True

# Initial setup

• self.hosts = self.read_static_hosts()
  

• self.update_dhcp_leases()
  

• update_hosts = True
  

• update_leases = True
  

• i = inotify.adapters.Inotify()
  
  

• i = inotify.adapters.Inotify([
  

• 	self.leases_file,
  

• 	self.fix_leases_file,
  

• 	self.hosts_file,
  

• ])
  

• for f in self.watches:
  

• 	i.add_watch(os.path.dirname(f), self.watches[f])
  
  

  for event in i.event_gen(): # End if we are requested to terminate if not self.running: break

• 	# Make pending updates once inotify queue is empty
  if event is None:
  

• 		if update_hosts:
  

• 			self.hosts = self.read_static_hosts()
  

• 			update_hosts = False
  

• 		if update_leases:
  

• 			self.update_dhcp_leases()
  

• 			update_leases = False
  	continue
  
  header, type_names, watch_path, filename = event
  
  

• 	# Update leases after leases file has been modified
  

• 	if "IN_MODIFY" in type_names:
  

• 		# Reload hosts
  

• 		if watch_path == self.hosts_file:
  

• 			self.hosts = self.read_static_hosts()
  

• 	file = os.path.join(watch_path, filename)
  

• 	if not file in self.watches:
  

• 		continue
  

• 	log.debug("Inotify %s: %s", file, " ".join(type_names))
  
  

• 		self.update_dhcp_leases()
  

• 	update_leases = True
  
  

• 	# If the file is deleted, we re-add the watcher
  

• 	if "IN_IGNORED" in type_names:
  

• 		i.add_watch(watch_path)
  

• 	if file == self.hosts_file:
  

• 		update_hosts = True
  
  

  log.info("Unbound DHCP Leases Bridge terminated")

-- 2.34.1