Brownfield import of vCenter 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. /var/log/vmware/vcf/domainmanager/domainmanager.log  on SDDC manager is showing the following error:

   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> this fails with the error: 

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

Environment

• VCF Operations 9.0.x & 9.1
• SDDC Manager 9.0.x & 9.1
• vCenter 8.x
• vCenter 9.0.x & 9.1

Cause

VCF Operations requires SSH (Port 22) access to the vCenter Server to validate environment attributes during the import process. The error occurs if SSH is disabled on the vCenter or if a firewall blocks Port 22.

Resolution

1. Log in to the vCenter Server Appliance Management Interface (VAMI) at https://####:5480.
2. Navigate to Access and verify SSH is Enabled.
3. From the SDDC Manager console, test connectivity to vCenter on port 22: 

   curl -v telnet://<vCenter-IP>:22

4. Ensure firewall rules allow bi-directional traffic on ports 22 and 443 between SDDC Manager/VCF Operations and vCenter.
5. Restart the workload domain import.

Additional Information

Enable or Disable SSH and Bash Shell Access

Enabling SSH access when vSphere Client and VAMI are unavailable