Backup application cannot communicate with one of the hosts with error: Failed to resolve certificate from ESXi host "hostname".

Products

• VMware vSphere ESXi

Issue/Introduction

• While performing a host discovery from backup application, the following error message is observed in the backup application.

Failed to resolve certificate from ESXi host "host_fqdn": A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond <host_IP-address>:443

• Telnet from the backup application to the ESXi host fails to connect.

# telnet <host_IPaddress> 443
Connecting To <host_IPaddress> ... Could not open connection to the host, on port 443: Connect failed

Environment

• vCenter 8.x, ESXi 8.x
• vCenter 9.x, ESXi 9.x

Cause

• As Port 443 is blocked between the ESXi host and the backup application, the backup application could not read the ESXi host's certificate and hence it failed to established a secure connection to the host resulting in the error message.

Resolution

• Open port 443 in the firewall between the ESXi host and the backup application.