Adding an ESXi host to a stretched cluster in VMware Cloud Foundation fails with the error "ADD_HOST_TO_HOST_GROUP_POST_VALIDATE_FAILED"

Products

• VMware SDDC Manager

Issue/Introduction

• The operation to add a new host into an existing stretched cluster within the Software-Defined Data Center (SDDC) environment fails, returning the error: "ADD_HOST_TO_HOST_GROUP_POST_VALIDATE_FAILED."
  
  
• Reviewing /var/log/vmware/vcf/domainmanager/domainmanager.log in SDDC manager, the below errors were observed:
  
  YYYY-MM-DD HH:MM:SS ERROR [vcf_dm,#######################,03f9] [c.v.v.c.f.p.a.i.AddHostsToHostGroupAction,dm-exec-4]  Post validate in add host to host group failed {0}
YYYY-MM-DD HH:MM:SS ERROR [vcf_dm,#######################,03f9] [c.v.e.s.o.model.error.ErrorFactory,dm-exec-4]  [QDCFJU] ADD_HOST_TO_HOST_GROUP_POST_VALIDATE_FAILED Post validate for add host to host group failed for cluster name cluster_name, host group name host_group_name and host names [host_fqdn] com.vmware.evo.sddc.orchestrator.exceptions.OrchTaskException: Post validate for add host to host group failed for cluster name cluster_name, host group name cluster_name and host names [host_fqdn]
YYYY-MM-DD HH:MM:SS DEBUG [vcf_dm,#######################,03f9] [c.v.e.s.o.c.ProcessingTaskSubscriber,dm-exec-4]  Collected the following errors for task with name AddHostsToHostGroupAction and ID ######-####-####-####: [ExecutionError [errorCode=null, errorResponse=LocalizableErrorResponse(messageBundle=com.vmware.vcf.common.vsphere.plugins.action.messages)]]

Environment

VCF 5.2.x
VCF 9.x

Cause

The issue stems from either the absence of host group names or case-sensitive discrepancies in the host group names within the vCenter cluster configuration.

Resolution

• Validate if the hostgroup being reported in the logs exists in the vCenter cluster and also match the case of the hostgroup.
• If the hostgroup is missing, create a new one as per the below naming convention. 
  
  Host group: 
  {Cluster-Name}_primary-az-hostgroup 
{Cluster-Name}_secondary-az-hostgroup

To configure the Host groups within vCenter UI:

• Select the cluster in vCenter UI.
• Configure Tab > VM/Host Groups.
• Select Add.
• Name the groups as per the above convention.
• Add the hosts into the primary and secondary hostgroups as per user requirement.
• Hit OK. 

Once this is done, restart the failed stretched cluster expansion task in SDDC manager.