Besides lots of other cool stuff it can do (including monitoring for a lot of your self hosted stuff), HomeAssistsnt has the Feedreader integration, which lets you poll RSS feeds. You can then create automations to send notifications to you through the HomeAssistsnt companion app.
Feedreader defaults to polling once per hour, but you can change this in the configuration.
It would help to be explicit yeah. If only for the reason that sometimes your issue could be caused by the way you set things up.
For reference, I have some LXCs with docker as an experiment( a privileged container with nesting=1 (also fuse=1 and keyctl=1, not sure if those help) and I haven’t had problems, but they’ve never needed a restore. I think unprivileged is where you will run into problems.
For doing what you want, you’ll want to bind mount your external drive. I’d recommend not using drive letter mounts (“/dev/sdc” for example) as those can change across reboots. Instead, use /dev/disk/by-id/<find-your-disks-id-and-put-it-here> which is the same no matter when the disk is mounted on the host. To make a bind mount, you have to edit the .conf file for your container on the host at /etc/pve/lxc/<vmid>.conf where the <vmid> is the container is number and then start the container back up. The disk will then appear in the container mounted at the path you specify. Check out the Proxmox docs for LXC bind mounts for info on how to configure that.