Backup to Proxmox Backup Server for one VM: dns error: failed to lookup address information: Name or service not known

[decibel83]

Hi,

I installed a Proxmox Backup Server and I configured a new backup storage on Proxmox VE 6.3-3.

Backups for all virtual machines works good, but for only one which returns the following error:

INFO: include disk 'virtio0' 'local-zfs:vm-101-disk-0' 32G
INFO: backup mode: snapshot
INFO: ionice priority: 7
INFO: snapshots found (not included into backup)
INFO: creating Proxmox Backup Server archive 'vm/101/2021-02-09T00:00:02Z'
ERROR: VM 101 qmp command 'backup' failed - backup connect failed: command error: error trying to connect: error connecting to https://pbs:8007/ - dns error: failed to lookup address information: Name or service not known
INFO: aborting backup job
ERROR: Backup of VM 101 failed - VM 101 qmp command 'backup' failed - backup connect failed: command error: error trying to connect: error connecting to https://pbs:8007/ - dns error: failed to lookup address information: Name or service not known
INFO: Failed at 2021-02-09 00:00:07

The strange thing is that all others VMs on the same PVE nodes backups on PBS without any errors.
I've already checked DNS things and the PVE node can resolve and correctly connect to https://pbs:8007.

Could you me help to understand what's wrong, please?

Thank you very much!
Bye

 

[dcsapak]

is it consistent? so if you backup again it does not work?

 

[decibel83]

is it consistent? so if you backup again it does not work?

Yes, it's been lasting since 3 days, when I activated backups on Proxmox Backup Server, and only for that VM.

I did not try to restart that VM because unfortunately it's the perimeter firewall and I can restart it only if it's really necessary.

All other VMs does not have such problem and backups regularly on PBS.

 

[dcsapak]

it's the perimeter firewall

is that firewall used for dns?

 

[decibel83]

is that firewall used for dns?

Yes!
So I'm answering myself: is that VM freezed at the beginning of the backup to PBS?

 

[oguz]

as a workaround you can add pbs in your /etc/hosts file in the PVE:

...

# pbs
ip.of.your.pbs pbs

then it should still resolve without the dns server being up at that time

 

[decibel83]

as a workaround you can add pbs in your /etc/hosts file in the PVE:

...

# pbs
ip.of.your.pbs pbs

then it should still resolve without the dns server being up at that time

Yes, I was thinking about this workaround.

But I want to understand why this happens.

Is the VM freezing during the backup?

Is it expected? I'm using the snapshot mode so I expect it does not freeze at all...

 

[lamp]

I am pretty sure that the VMs freeze during backup. I have HA DNS servers on separate machines across the cluster and despite this, my entire DNS goes down temporarily during backup. I am looking for some workaround myself