Enable NIS extensions (rfc2307) on Samba 4 AD after installation

I'm testing out our samba 4 migration process and when the initial forest/domain was created, it was created without using --use-rfc2307:

sudo samba-tool domain provision \
              --domain netdirect \
              --realm=ad.netdirect.ca \
              --function-level=2008_R2

Now that it's in place and we have machines joined, what do I need to do to add the unix attributes and NIS maps to an existing samba4 domain so that we can use the rfc2307 features?

The schema extensions from ypServ30.ldif must be added:

$ kinit [email protected]
Password for [email protected]

$ sed -e 's/${DOMAINDN}/dc=AD,dc=NETDIRECT,dc=CA/g'  \
      -e 's/${NETBIOSNAME}/NETDIRECT/g'              \
      -e 's/${NISDOMAIN}/NETDIRECT/g'                \
      /usr/share/samba/setup/ypServ30.ldif | ldbmodify -H ldap://ad1.ad.netdirect.ca --option="dsdb:schema update allowed=true" -k yes -i
Modified 55 records successfully

Then, add to the [global] section of /etc/samba/smb.conf:

idmap_ldb:use rfc2307 = yes

Restart samba (smbcontrol all reload-config) and you should be good to go.

(Thanks to Rowland Penny for the initial directions)