samba - Apr 2018 - The 'not-always-on' infrastructure at home and Samba4 AD DC's..

Hi everyone,

Apoligies in advance, this will be a bit long but I'm hoping to get some 
guidance and hints on usual practices for using Samba4 AD DC as an Idm for 
W10 laptops that might be on the road elsewhere.. As much as I have been 
using samba for file serving, a Samba AD DC is something new to me.

I built a small Samba AD DC infrastructure to serve UIDs and Passwords (4 
VMs on 4 KVM hosts). My problem is that not all Samba DC's will always be 
turned on. Out of the 4 KVM hosts, 1 or 2 are going to be turned off quite 
often (especially in the summer), another one is going to be up half of the time
on average while the first server will most likely average 95% uptime.

The key metric here is that at least -one- hypervisor/router will -always- 
be available at any given time and this will be sufficient to provide all 
neded services. Also there isn't any type of shared storage (only 
replicated storage when two nodes with a replication schedule happen to be 
on at the same time).

This strange setup has been serving a family of 5 for the past 10 years, 
providing DNS, NFS, SMB, Squid+UfdbGuard, NAT, IDS, filtering, etc..

Most of the family laptops now run W10 (Microsoft Office at school is 
still a hard requirement in some places) while most other boxes use 
Fedora with the infra servers running RHEL7.

Wanting to provide centralized password management to the teenagers and 
not feeling like managing local user accounts on their Windows laptops, I 
opted for Samba as an AD DC. To this effect, I built 4 RHEL7 VMs (one per 
physical server because I have no shared storage). I used Wing's 4.6.14 
rpms (http://wing-repo.net/wing) because RHEL7's samba doesn't do AD DC 
yet.

So I find myself with the following setup:

- KVM Host #0 -> VM guest DC0	(expected uptime: around 95%)
- KVM Host #1 -> VM guest DC1	(expected uptime: around 90%)
- KVM Host #2 -> VM guest DC2	(expected uptime: around 25-50%)
- KVM Host #3 -> VM guest DC3	(expected uptime: around 10-25%)

I setup the 4 VMs (DC0, DC1, DC2, DC3) in an AD just fine and was able to 
verify proper configuration/replication. ( Win10 connectivity, drs 
showrepl, RSAT access and usability).

- Is the 4*DC setup a good or a bad idea in that use-case? I decided 
against a 2*DC setup because there may be times both DC0 and DC1 might be turned
off at
the same time.

- Aside from some TCP timeouts caused by the unavailability of some of the 
IPs (the AD A DNS record will always show 4 IPs, regardless of which 
servers are turned off), what other issues could happen on the laptops?

- Is there a hard limit on the number of days that those W10 laptops can 
go without being connected to any of Samba DC's (think remote summer job) 
and keep using cached credentials? (or is it just like with an ordinary 
AD)

Any do's and don'ts would be much apreciated. Thanks in advance.

Regards,

Vincent

On Mon, 26 Mar 2018 16:18:55 -0400 (EDT)
"Vincent S. Cojot via samba" <samba at lists.samba.org> wrote:
> I built a small Samba AD DC infrastructure to serve UIDs and
> Passwords (4 VMs on 4 KVM hosts). My problem is that not all Samba
> DC's will always be turned on. Out of the 4 KVM hosts, 1 or 2 are
> going to be turned off quite often (especially in the summer),
> another one is going to be up half of the time on average while the
> first server will most likely average 95% uptime.
The problem here is that the AD data is replicated between DCs and if a
DC is turned off, the logs will start filling up with 'cannot find
DC?' type messages.
The laptops are the least of your worries, the passwords will remain
valid until they connect to a DC again.

I think you need to reconsider this, perhaps just use one DC on bare
metal, you will not get replication errors if there isn't another DC to
replicate to and you will be able to turn this off when required. You
will have to backup this DC regularly, just in case of a computer
failure, but these would have to be stored off the DC, perhaps on a
portable HD.
 
Rowland