I ran into this issue yesterday, and I couldn't find anyone with this issue that actually solved it. To give you all some context, we have a handful of two-host clusters. Each cluster is currently configured for non-shared storage, utilizing the storage on the servers themselves to run the VMs. Replication is enabled between the hosts for HA. This was all a proof-of-concept setup with hardware "laying around" after having received our VMware renewal late last year; we will be running a more Proxmox-specific setup later down the road.
Our Proxmox hosts are all configured to not allow root access via SSH. I am not sure if this is the default or not, as another coworker set everything up. For VEEAM backup to work with Proxmox, there is info out there that tells you that you need to allow root access to the hosts/cluster in order for VEEAM backup to work successfully. What they don't tell you is that the VEEAM backup worker also needs root access via SSH to the hosts as well. If you have "Permitrootlogin yes" in "/etc/ssh/sshd_config" on your hosts, you shouldn't run into this problem. If you try to limit this to a specific IP address by adding your VEEAM backup server IP as being able to login with root (Match Address), all of the host/cluster/worker tests will return as a success, but an actual backup will still error out with "Failed to reach hypervisor". You can see if what I am describing is your problem by looking by browsing to "%ProgramData%\Veeam\Backup\Plugins\PVE\Backup\BACKUP_JOB_NAME\SERVER_NAME_INSTANCE\", opening up the ZIP containing the failed backup job, and opening up the log that has your server name in it.
In the log, you should see an error that looks like this:
2024-10-17 09:46:30.5492 00006 [1529] ERROR | [ProxmoxBackupManager]: Failed ssh connect to Proxmox node SERVER_NAME with ip PROXMOX_HOST_NAME:22. Error: Permission denied (password).: Renci.SshNet.Common.SshAuthenticationException: Permission denied (password).
Once you add in the additional IP address of the worker in the sshd_config file of your host/s like what is shown below, and then restart the sshd service, the backup job should now be able to start and complete.
Addition to sshd_config:
Match Address 10.10.10.10
PermitRootLogin yes
Our Proxmox hosts are all configured to not allow root access via SSH. I am not sure if this is the default or not, as another coworker set everything up. For VEEAM backup to work with Proxmox, there is info out there that tells you that you need to allow root access to the hosts/cluster in order for VEEAM backup to work successfully. What they don't tell you is that the VEEAM backup worker also needs root access via SSH to the hosts as well. If you have "Permitrootlogin yes" in "/etc/ssh/sshd_config" on your hosts, you shouldn't run into this problem. If you try to limit this to a specific IP address by adding your VEEAM backup server IP as being able to login with root (Match Address), all of the host/cluster/worker tests will return as a success, but an actual backup will still error out with "Failed to reach hypervisor". You can see if what I am describing is your problem by looking by browsing to "%ProgramData%\Veeam\Backup\Plugins\PVE\Backup\BACKUP_JOB_NAME\SERVER_NAME_INSTANCE\", opening up the ZIP containing the failed backup job, and opening up the log that has your server name in it.
In the log, you should see an error that looks like this:
2024-10-17 09:46:30.5492 00006 [1529] ERROR | [ProxmoxBackupManager]: Failed ssh connect to Proxmox node SERVER_NAME with ip PROXMOX_HOST_NAME:22. Error: Permission denied (password).: Renci.SshNet.Common.SshAuthenticationException: Permission denied (password).
Once you add in the additional IP address of the worker in the sshd_config file of your host/s like what is shown below, and then restart the sshd service, the backup job should now be able to start and complete.
Addition to sshd_config:
Match Address 10.10.10.10
PermitRootLogin yes