How does restarting a deleted node break a cluster

[spamsam]

Hi,

According to: https://pve.proxmox.com/pve-docs/pve-admin-guide.html#_remove_a_cluster_node

It states the following:

Important    As mentioned above, it is critical to power off the node before removal, and make sure that it will not power on again (in the existing cluster network) with its current configuration. If you power on the node as it is, the cluster could end up broken, and it could be difficult to restore it to a functioning state.

Out of interest what exactly can cause the cluster to go fubar if the a deleted node is accidentally restarted?

 

[mira]

Since you've deleted the node from the cluster at this point, all nodes still in the cluster won't know anything about the removed node.
When it comes online, it will send packets like nothing happened and this will most likely break the cluster communication (corosync).

 

[lost_avocado]

Hi, its an old thread but I cant find the answer, so I just try
If the above mentioned is the case, wouldn't it be possible to remove all cluster cluster config and start all over again, creating cluster and re-add nodes?

 

[mira]

Yes, that's possible as well.

But note that hosts with guests (VMs, CTs) can't be joined to a cluster. So those would need to be backed up and then restored once the host is part of a cluster.

 

[esi_y]

Isn't there a difference between "zombie" node suddenly sending around irrelevant corosync traffic (that should not matter) and the said zombie actually sending traffic that clashes with another (by that time) new/replacement node that is actually the (only time of a real) problem?

 

[fabian]

no, as soon as a "former" node that still has the right corosync key (or, if you switched from the recommended, default encrypted config to an unencrypted one, even without) tries to talk to the cluster it can disrupt operations, there doesn't need to be a new node in its place (although that likely makes things worse, especially if you really re-use the nodeid and/or hostname).