[pve-devel] HA Migration on shutdown/reboot

[Alexandre DERUMIER]

Hi all,

in our last week training session, students also ask for the same feature,

with a real problem, when we have 2 hosts in same ha group, with differents priority,

and user want to do maintenance/reboot, he would like to migrate all vms on other node,
before reboot. But currently manually migrating vms (with migrate_all for example),
the HA is migrated them back before the migrate all is finished,
so it's super difficult to have the node empty for reboot.


Maybe could we first add some kind of "maintenance mode" flag on a node, which mean than vms
can't be migrated back to it. (we virtually remove it from HA groups until maintenance mode is removed).
and user could at least migrate them manually.



For auto migrate on shutdown,

I think the most difficult part is to how to choose the targetnode where to migrate the vm.
Maybe could we choose another nodes of a HA group (excluding the node with maintenance mode)

Another thing which could be great (even with HA), could be to auto choose targetnode based on cpu/ram current usage,
like  "migrate ... --targetnode  node_with_lower_ram,  node_with_lower_cpu."




----- Mail original -----
De: "Bastian Sebode" <b.sebode at linet-services.de>
À: "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Mardi 28 Mai 2019 02:40:03
Objet: [pve-devel] HA Migration on shutdown/reboot

Hello Proxmox Team, 

I'm wondering why there is no option "migrate" for the shutdown_policy 
available. 

I looked a bit through the code and found create_migrate_worker() in 
PVE/API2/Nodes.pm, which is used in mass migration. Can't this be used 
in PVE/HA/LRM.pm when shutdown_policy = "migrate"? 

You know that servers take from 1 to 10 minutes to reboot. So the 
interruption by freezing, shutting down and starting on another node in 
HA setup seems not logic to me and will take a long time to recover the 
service. 
-> shutdown of databases, mounts, guest os 
-> shutdown of host 
-> start on other host 

Migration would keep the service running all the time - I guess in HA 
activated Environments online migration is mostly possible - and would 
also accelerate the shutdown of the host, because the VMs don't have to 
shut down on that host. 

Defining the Target Node could rely on the HA Groups priority and if not 
in HA you could still freeze and shutdown a VM or migrate to least used 
node - I remember Thomas already wrote about this and the problems 
behind - or even ask where to migrate. 

Right now the only way to keep services in HA online all the time 
through a node reboot, is to change the HA Group, so the service gets 
correctly migrated by crm. But that also has to be undone after the reboot. 

Okay, right now LXC came to my mind... I know there's no online 
migration, but am speaking for KVM now. ;-) Freeze is also applicable here. 

Probably it's not that easy to implement as I think on top, but do you 
already think of a feature like this? Or is there any other way to 
update my HA activated Cluster without service downtime and without the 
HA Group changing? 

Thanks so far for PVE! <3 
Peace 
Bastian 

-- 
Bastian Sebode 
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