BIG cluster questions

[Eneko Lacunza]

Hi all,

We're currently helping a customer to configure a virtualization cluster 
with 88 servers for VDI.

Right know we're testing the feasibility of building just one Proxmox 
cluster of 88 nodes. A 4-node cluster has been configured too for 
comparing both (same server and networking/racks).

Nodes have 2 NICs 2x25Gbps each. Currently there are two LACP bonds 
configured (one for each NIC); one for storage (NFS v4.2) and the other 
for the rest (VMs, cluster).

Cluster has two rings, one on each bond.

- With clusters at rest (no significant number of VMs running), we see 
quite a different corosync/knet latency average on our 88 node cluster 
(~300-400) and our 4-node cluster (<100).


For 88-node cluster:

- Creating some VMs (let's say 16), one each 30s, works well.
- Destroying some VMs (let's say 16), one each 30s, outputs error 
messages (storage cfs lock related) and fails removing some of the VMs.

- Rebooting 32 nodes, one each 30 seconds (boot for a node is about 
120s) so that no quorum is lost, creates a cluster traffic "flood". Some 
of the rebooted nodes don't rejoin the cluster, and WUI shows all nodes 
in cluster quorum with a grey ?, instead of green OK. In this situation 
corosying latency in some nodes can skyrocket to 10s or 100s times the 
values before the reboots. Access to pmxcfs is very slow and we have 
been able to fix the issue only rebooting all nodes.

- We have tried changing the transport of knet in a ring from UDP to 
SCTP as reported here:
https://forum.proxmox.com/threads/proxmox-6-2-corosync-3-rare-and-spontaneous-disruptive-udp-5405-storm-flood.75871/page-2
that gives better latencies for corosync, but the reboot issue continues.

We don't know whether both issues are related or not.

Could LACP bonds be the issue?
https://pve.proxmox.com/pve-docs/pve-admin-guide.html#sysadmin_network_configuration
"
If your switch support the LACP (IEEE 802.3ad) protocol then we 
recommend using the corresponding bonding mode (802.3ad). Otherwise you 
should generally use the active-backup mode.
If you intend to run your cluster network on the bonding interfaces, 
then you have to use active-passive mode on the bonding interfaces, 
other modes are unsupported.
"
As per second line, we understand that running cluster networking over a 
LACP bond is not supported (just to confirm our interpretation)? We're 
in the process of reconfiguring nodes/switches to test without a bond, 
to see if that gives us a stable cluster (will report on this). Do you 
think this could be the issue?


Now for more general questions; do you think a 88-node Proxmox VE 
cluster is feasible?

Those 88 nodes will host about 14.000 VMs. Will HA manager be able to 
manage them, or are they too many? (HA for those VMs doesn't seem to be 
a requirement right know).


Thanks a lot
Eneko


      EnekoLacunza

CTO | Zuzendari teknikoa

Binovo IT Human Project

	943 569 206 <tel:943 569 206>

	elacunza at binovo.es <mailto:elacunza at binovo.es>

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