One of our clients has a proxmox cluster that they have not updated in quite some time. Their cluster consists of 3 hosts with the following versions (OS is Debian Jessie):
proxmox-ve: 4.1-34 (running kernel: 4.2.6-1-pve)
pve-manager: 4.1-5 (running version: 4.1-5/f910ef5c)
pve-kernel-4.2.6-1-pve: 4.2.6-34
lvm2: 2.02.116-pve2
corosync-pve: 2.3.5-2
libqb0: 0.17.2-1
pve-cluster: 4.0-31
qemu-server: 4.0-47
pve-firmware: 1.1-7
libpve-common-perl: 4.0-45
libpve-access-control: 4.0-11
libpve-storage-perl: 4.0-38
pve-libspice-server1: 0.12.5-2
vncterm: 1.2-1
pve-qemu-kvm: 2.5-3
pve-container: 1.0-39
pve-firewall: 2.0-15
pve-ha-manager: 1.0-19
ksm-control-daemon: 1.2-1
glusterfs-client: 3.5.2-2+deb8u1
lxc-pve: 1.1.5-6
lxcfs: 0.13-pve3
cgmanager: 0.39-pve1
criu: 1.6.0-1
They would like to update their servers to the latest versions available for Jessie. But possible downtime time must be kept at minimum possible (a handful of hours at most). What steps are recommended for such a scenario? Is it possible to upgrade the cluster a node at a time and have them re-clustering as they update to the new version? Are there any risks involved in this? They do have a community subscription, thus access to the non-free repositories and a further upgrade to stretch is also likely (though it will happen in a second step).
proxmox-ve: 4.1-34 (running kernel: 4.2.6-1-pve)
pve-manager: 4.1-5 (running version: 4.1-5/f910ef5c)
pve-kernel-4.2.6-1-pve: 4.2.6-34
lvm2: 2.02.116-pve2
corosync-pve: 2.3.5-2
libqb0: 0.17.2-1
pve-cluster: 4.0-31
qemu-server: 4.0-47
pve-firmware: 1.1-7
libpve-common-perl: 4.0-45
libpve-access-control: 4.0-11
libpve-storage-perl: 4.0-38
pve-libspice-server1: 0.12.5-2
vncterm: 1.2-1
pve-qemu-kvm: 2.5-3
pve-container: 1.0-39
pve-firewall: 2.0-15
pve-ha-manager: 1.0-19
ksm-control-daemon: 1.2-1
glusterfs-client: 3.5.2-2+deb8u1
lxc-pve: 1.1.5-6
lxcfs: 0.13-pve3
cgmanager: 0.39-pve1
criu: 1.6.0-1
They would like to update their servers to the latest versions available for Jessie. But possible downtime time must be kept at minimum possible (a handful of hours at most). What steps are recommended for such a scenario? Is it possible to upgrade the cluster a node at a time and have them re-clustering as they update to the new version? Are there any risks involved in this? They do have a community subscription, thus access to the non-free repositories and a further upgrade to stretch is also likely (though it will happen in a second step).
