Corosync & variable number of nodes in a cluster


May 21, 2019

I currently have a cluster of 2 promox with "two_node : 1" in corosync quorum setting. This cluster will grow to 6 servers. However, for reasons of maintenance it is possible that only 1 node is active on the 6.

Because of the qorum vote, it is impossible to make a 2 node cluster work if one of the two nodes is stopped, two_node is the way to do it.

In order to avoid that the VMs stop I want to set up an option similar to two_node but I don't know which one to choose. Currently "last_man_standing: 1" seems to me the best solution.

Is this the best solution?

reasons of maintenance it is possible that only 1 node is active on the 6.

Hmm, normally it should be possible to do maintenance on one to maximal two nodes, so the rest can stay quorate without enabling experimental features.

Just as a hint, those things like "two_node" and especially "last_man_standing" are all not really supported by Proxmox VE, so your a bit on your own..

IF you use "last_man_standing" I'd at least always add "wait_for_all" this reduces the chance for split brain cluster a lot..

Else, closely reading the "votequorum" manpage should give a lot of information regarding this.
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Reactions: chrisimm
Thank you for your answer.

If I understand correctly, the two_node option should not be enabled.

Let's assume that this option is removed from the configuration, what are the consequences if the cluster is cut in two? 3 nodes on one side and 3 nodes on the other?

Thanks for your help.


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