vCenter VAMI backup fails with error "Failed to create backup directory on backup server"

Products

• VMware vCenter Server

Issue/Introduction

/var/log/applmgmt/backup.log contains the following:

Error: sftp cmd failed. RC: 2, Err: curl: (2) Failure establishing ssh session: -43, Failed getting banner

Other symptoms:

• You are successful in performing SSH from vCenter to backup server
• Within backup server logs, it claims that vCenter terminated the session after failed backup attempts

Environment

vCenter 7.0.x
vCenter 8.0.x

Cause

A firewall between the vCenter and backup server may be interpreting the large quantity of curl commands originating from the vCenter as a brute force attack, and will temporarily block those connections shortly after initiating the backup.

This issue was initially discovered within a network utilizing a Palo Alto firewall.

Resolution

If you use a Palo Alto firewall (or another type of restrictive firewall) and experience this issue, investigate the firewall logs. If necessary, make an exception for this type of traffic originating from your vCenter.