Comment 10 for bug 1720887

That is very interesting Chris.
As it should not be on 1024/4096 at all.

The limit was not set back in libvirt 2.5 and before, so older versions had a higher limit - that much is true.
I checked and it has
    Artful: Max open files 8192 8192 files
Pre-Artful: Max open files 1048576 1048576 files

But both limits are way above yours.

Your case has ~4 files per guest, but with the right limit that should be enough to close to 2k guests.

I'd suggest two things:
1. I'll discuss upstream to raise the 8192 to 16384 as it seems Openstack (as a common setup) has 4 files per guest.
I'll do that and link the Mailing List entry here

2. We need to find why you have a limit applied even lower than what the service file configures.
   @Chris - can you have a look on that system why that could be so low - any extra limits
    applied somewhere?
    Does the virlogd service file have the 8192 by default - if it has 1024/4096 what changed it?
    If it has 8192, can you see on the system where the 1024/4096 might come from?