VUM scan fails with error "VMware vSphere Update Manager had an unknown error. Check the events and log files for details"

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• Scanning an ESXi host  fails with error "VMware vSphere Update Manager had an unknown error. Check the events and log files for details"
• vmware-vum-server-log4cpp.log on the VUM server  shows the below errors:
  • [2019-11-26 23:38:27:794 'SingleHostUpgradeScanTask.SingleHostUpgradeScanTask{321}' 139906224486144 ERROR] [singleHostUpgradeScanTask, 277] Error while scanning: Connection refused: The remote service is not running, OR is overloaded, OR a firewall is rejecting connections.
• vmware-vum-server.log on the VUM server  shows the below errors:
  • 2019-11-27T01:40:47.875Z warning vmware-vum-server[23811] [Originator@6876 sub=Default] Failed to connect socket; <io_obj p:0x00007f3e20026fd0, h:25, <TCP '<IP of VUM server> : 37082'>, <TCP '<IP of ESXi host> : 80'>>, e: 111(Connection refused)
• Running nc (netcat) command on the ESXi host port 80 fails with connection refused error:
  • nc -tv <IP of ESXi Host> 80

<FQDN of ESXi host> [<IP of ESXi Host>] 80 (http): Connection refused

Environment

VMware vSphere Update Manager 6.7.x

Cause

VUM requires port 80 to be open between the VUM/vCenter server and the ESXi host. If a Firewall is blocking port 80, then you see these errors.

Resolution

Open port 80 on the Network Firewall between VUM/vCenter and ESXi hosts