External Corosync QDevice via WAN/VPN

[Nyctophilia]

Hello Proxmox-community,

I want to develop a 2-node cluster-concept.

Is it possible to have a QDevice via VPN, for example in a datacenter?
Multiple ISP-uplinks (DSL, Cable, Fiber, LTE) with failover are mandatory of course.
I'm not talking about datacenter to datacenter interconnect fiber links.

What are the maximum latencies/paketloss values? Are they tweakable to some point? I know the documentation says latencies over 2ms are no problem, but it could also mean under 10ms.
What if the QDevice is offline for a few seconds/minutes because of ISP-failover? Any experiences with a setup like this?

I know there are variants with RaspberryPis/NAS-boxes + Container as a third local QDevice, but I'm looking for another approach to this.

Thank you in advance!

 

[aaron]

I cannot give you an answer on how long the latency to the QDevice can be.

What if the QDevice is offline for a few seconds/minutes because of ISP-failover? Any experiences with a setup like this?

As long as both nodes are running you are fine as they can still form a quorum. Should one of the two nodes fail and the QDevice is not reachable you will have no quorum on the remaining node. Or both will not have quorum should the corosync link between them fail.

What happens next depends on having any HA resources or not.

The simple case is without any HA resources defined. Then all VMs will continue to run but you won't be able to make any changes to the cluster or start, stop guests.

If you have HA enabled on both nodes you will have the problem that a node that is not part of the quorum will fence itself (hard reset) after ~2 minutes.