Brownfield import of vCenter 8 into VCF Operations as a workload domain fails with error "Http failure response for https://<vcfopsfqdn>/vcf-operations/plug/sddc-76/plugin/api/v1/sddcs/imports/validations: 504 OK"

Products

• VCF Operations/Automation (formerly VMware Aria Suite)

Issue/Introduction

1. Sign into VCF Operations UI → Navigate to Inventory → Basic View  → Expand VCF Instances  → Select the instance you require  → Click on Add Workload Domain  → Import a vCenter  → Fill in Domain Name  → Enter in the correct vCenter details to specify a vCenter → Precheck fails with the error "Http failure response for https://<vcfopsfqdn>/vcf-operations/plug/sddc-76/plugin/api/v1/sddcs/imports/validations: 504 OK" 
2. Error in /var/log/vmware/vcf/domainmanager/domainmanager.log  in SDDC is similar to 

   2025-11-19T12:54:57.906+0000 DEBUG [ucf_dn, #################,####] [c.u.e.s.c.uti1. Local ProcessService,http-nio-127.0.0.1-7200-exec-51 Error Output: ssh: connect to host <vCenterFQDN> port 22: Connection refused
   2025-11-19T12:54:57.907+0000 WARN [ucf_dn, ############,####] [c.v.evo.sddc.common.util.SshKeyScan, http-nio-127.0.0.1-7200-exec-51 Fail to get host key for <vCenterFQDN>:22 with host key algorithms rsa-sha2-512,rsa-sha2-256

3. Open SSH to SDDC Appliance as VCF user from there try to SSH to vCenter as root with the command ssh root@<vCenterFQDN> fails with the error: 

   ssh: connect to host <vCenterFQDN> port 22: Connection refused

Environment

VCF Operations 9.x

Cause

vCenter port 22 is closed 

Resolution

Enable SSH for the affected vCenter.  If you have access to the vCenter VAMI you can use the following documentation as a guide Enable or Disable SSH and Bash Shell Access or if you do not have access you can use the following KB as a guide Enabling SSH access when vSphere Client and VAMI are unavailable