vCenter Upgrade fails through SDDC Manager with error "Unable to connect to the given vCenter or ESXi on its SDK endpoint"

Products

• VMware SDDC Manager

Issue/Introduction

When attempting a RDU (Reduced Downtime Upgrade) through SDDC Manager the vCenter upgrade fails on the Precheck stage with error : "Unable to connect to the given vCenter or ESXi on its SDK endpoint" . 

In the vCenter logs we may see the following: 

/var/log/vmware/vlcm/vlcm.log: 

2025-10-07T18:14:43.488Z info vlcm [logger/teelogger.go:54] [opID=vapi] Message formatter created for en, en, UTC, 2, SHORT_DATE_TIME
2025-10-07T18:14:43.488Z error vlcm [engine/engine.go:1050] [ObjectID=22[1].2] wfengine: execute [<22[1].2:A> vm.Destroy(target)] error: com.vmware.vapi.std.errors.error
2025-10-07T18:14:43.489Z info vlcm [locerrors/vapierrors.go:36] [opID=68e3f62e] Parsing vAPI error json to real object
2025-10-07T18:14:43.489Z info vlcm [locerrors/vapierrors.go:45] [opID=68e3f62e] Error type: map[Data:null ErrorType:"ERROR" Messages:[{"Id":"vcenter.deployment.migration_upgrade.container.remote_sdk_unable_to_connect","DefaultMessage":"Unable to connect to the given vCenter or ESXi [vc_fqdn:443] on its SDK endpoint.","Args":[],"Params":{"0":{"S":"[vc_fqdn:443]","Dt":null,"I":null,"D":null,"L":null,"Format":null,"Precision":null}},"Localized":"Unable to connect to the given vCenter or ESXi [vc_fqdn:443] on its SDK endpoint."},{"Id":"vcenter.deployment.migration_upgrade.container.remote_sdk_unable_to_connect.resolution","DefaultMessage":"Ensure that the current vCenter can reach the given vCenter or ESXi, that there are no authentication issues, and that all the services are working correctly on the remote server.","Args":[],"Params":null,"Localized":"Ensure that the current vCenter can reach the given vCenter or ESXi, that there are no authentication issues, and that all the services are working correctly on the remote server."}]]
2025-10-07T18:14:43.489Z info vlcm [locerrors/vapierrors.go:63] [opID=68e3f62e] Error type: ERROR

Environment

VMware Cloud Foundation 5.2.x

Resolution

When configuring the vCenter upgrade, configure with the 'vCenter Regular Upgrade' instead of the 'vCenter Reduced Downtime Upgrade' option.