[Samba] Custom nsupdate command

[Hef]

My aim is to write an nsupdate replacement that updates dns entries through
the linode web api  for use in samba4.

In smb.conf, I have:

[global]
allow dns updates = True
nsupdate command = /usr/local/bin/dns_update_script.py

Currently, dns_update_script.py only writes to a log file when it is
called, copying its std input to a log file.

Calling samba_dnsupdate doesn't seem to call the dns_update_script.py at
all.

Are there other settings I need to check?
Do I have a misunderstanding about what is supposed to happen or when the
samba_dnsupdate command gets called?
Is there any information I should post that will help debug getting the
dns_update_script.py called?

--hef