That being said, Thanks to VATES and all who have worked on solutions for this! It truly benefits everyone!

I’ve been configuring NUT on XCP-ng 8.3 and had some trouble finding proper documentation. However, after going through the messages in this forum, I created a document that I believe might help others set up the NUT client on XCP-ng 8.3:
https://github.com/samuel-olavo/xcp-ng-nutclient

This method worked for me — tested and confirmed.

Thanks everyone!

In order to run NUT as a monitor to shut down your XCP-ng hypervisors it is no longer sufficient to just install nut-client and enable nut-monitor.

You also need to install nut and enable nut.target or nut-monitor won't autostart. There won't be anything in journalctl either, since it isn't even trying to start - the thing that tells it to do so is the nut.target and if that's missing nothing will ever trigger.

yum install nut nut-client --enablerepo=epel

make your edits in nut.conf and upsmon.conf then

systemctl enable nut.target 
systemctl enable nut-monitor 
systemctl start nut-monitor

SBCs are everywhere these days. Using a Raspberry Pi as the NUT Server in a homelab or a flavor of a more robust server for NUT seems like a solid choice. No USB passthrough to worry about, uptime on a 1500VA+ UPS, forget about it! There are a handful of guides how to get it running for a Pi or anything else (including this post).

As I think this though, I would still feel ok with another external device watching, waiting, and notifying me on a successful power off of any number of my hosts and VMs. Not all enterprises or homelabs can afford (even if their appetites want it) to get enterprise level power automations. We have our power. Break the chain. @olivierlambert

And as usual, contributions are always welcome!

For example, we are running server rooms at our main production sites worldwide (no data centers, no colo, all on-site). Each features a three VMware hosts cluster with shared storage, backup, switches, and firewalls in an air-conditioned server room with adequate fire prevention/protection. All have two power feeds (A and B or left and right as Olivier called them) and all systems have dual PSUs, but the sites usually have only one power supplier and no generators.

Feed A goes to an UPS and feed B directly to the power line. If the power goes down, the UPS automatically triggers the vCenter, storage and backup to shut down when the UPS remaining runtime is below a certain threshold.

But I can perfectly understand Oliviers reasoning and there are workarounds. It all depends on your risk appetite (if that is a word in English).

Also, everything is backed by UPS (both feeds) inside the building, and then diesel generators are taking the load after 10/15 minutes (diesel takes few minutes to start).

So in a colo, you will never have to get your own UPS.

Sadly, this use case is more meant for "non server-grade", where your machine isn't hosted in a datacenter (which is the default XCP-ng target/market).

However, I'm not against helping people doing the configuration or having an official guide to document it (I mean, in our doc)

Keep in mind we are always trying to find a balance between maintaining something (meaning time+money over other features) vs where the money is coming from (companies paying for support). If we pre-install all of this, it means we'll need to maintain it, while we still have a huge backlog of critical feature for our main (paying) target I hope you understand. Also, if we succeed and continue to grow that way with a far larger team than today, we could probably use that extra money from companies to improve integrations for the rest. But before doing it, we need to focus.

yum -y install nut-client --enablerepo=epel

It would be cool if xcp-ng came pre-installed with nut-client and a default configuration that shuts down the xen server & turns off the ups after it finishes shutting down... similar to how truenas has a service which can be enabled to do so. You'd have to configure it of course, with the nut server to monitor, credentials, and some other options such as whether to actually powerdown the ups after shutting down or not, but maybe through a nice gui after turning it on. Seems like everyone should be using this setup ... just a matter of time till they are ready to.

Another reason this would be nice to be integrated, is that docs recommend setting up a user account for nut, one for the monitor so clients can access and another for the shutdown so one of the watchers doesn't change the shutdown script & nut provides a file that indicates when the ups should shutdown, so having that be the same on all xcp-ng systems rather than custom solution would be good.

Network UPS Tools
Installation on XCP-ng Host

At first: Connect your UPS.
Then run this commands to install NUT:

yum update

yum –enablerepo=* install epel-release

yum install nut

yum install nut-client

cd /etc/ups

wget https://github.com/serrc-techops/NUT-Configuration/blob/master/slave/xen/xen-shutdown.sh

chmod +x xen-shutdown.sh

Important Commands

• upsc apcups (check UPS connection)

• systemctl restart nut-server
  (NUT-server reboot) | (Use this to apply configuration changes and to connect the UPS after System startup)

• systemctl restart nut-monitor (NUT-monitor restart)

• nut-scacnner -U (shows connected devices)

Configure the files stored in /etc/ups like this:
upsmon.conf

RUN_AS_USER root
MONITOR apcups@localhost 1 admin [PASSWORD] master
SHUTDOWNCMD „/etc/ups/xen-shutdown.sh“

nut.conf

MODE=netserver

ups.conf

pollinterval = 1
maxretry = 3
[apcups]
driver = usbhid-ups 
#->when you use USB devices
port = auto
desc = „[NAME]“
vendorid = [VENDORID]
productid = [PRODUCTID]
serial = „[SERIALNO]“

upsd.conf

LISTEN 0.0.0.0 3493

upsd.users

[admin]
password = [PASSWORD]
actions = set
actions= fsd
instcmds = ALL

Finish config Changes

systemctl restart nut-server
systemctl restart nut-monitor

Finished
Good to know: You can now also connect to your NUT server via the pfSense plugin by using the credentials in uspd.users to have a gui for your UPS. To do this you have to open up Port 3493 on your host.
Run this command to open the Port:

iptables -I INPUT -p tcp -m tcp --dport 3493 -j ACCEPT

Then save your changes to a config file and adjust Year, Month and Day in the config name. In my case it's the 22th of december in 2022:

iptables-save > /etc/sysconfig/iptables
mkdir /etc/iptables/
iptables-save > /etc/iptables/rules_2022-12-22_INPUT_ACCEPT_3493_NUT.v4 --> Optional, extra saving for Backups.

I recommend using this convention of naming your rule files. Its a lot easier to track your changes and to restore files.

On issuing the command:

[21:56 xenserver1 ups]# ./xen-shutdown.sh 

All VMs shutdown EXCEPT for the Xen Orchestra. I tried remove and reinstall Xen Tools

apt install xe-guest-utilities

I'm on Ubuntu 18.04

Is there something that should be done with Xen Orchestra? Like I said, all other VMs shutdown quickly and properly. I only have Ubuntu 18.04 and one instance of FreePBX. FreePBX shutdown properly too.

Update: it seems that after 5-10 minutes (not sure yet as I haven't timed it), the entire XCP-NG does shutdown but not sure if it was a forced of graceful shutdown on the VM running XO.