After upgrading from vSphere 5.5 to 6.0 error "503 Service Unavailable (Failed to connect to endpoint: [N7Vmacore4Http16LocalServiceSpecE:0x1f06b760] _serverNamespace = / _isRedirect = false _port = 8309)"

Dear community,

we were running vSphere 5.5 on Fujitsu RX300 with two local disks and conencted via iSCSI to a Synology SAN. After entering maintenance mode with the vSphere 5.5, I rebooted to official ISO and run through the uopgrade process without any errors. After next reboot I could not access the systemneithzer by the vSphere Client not by HTTP interface. The error show by direct browser access is: "503 Service Unavailable (Failed to connect to endpoint: [N7Vmacore4Http16LocalServiceSpecE:0x1f06b760] _serverNamespace = / _isRedirect = false _port = 8309)"

Login to the system is possible by ESXCli and ssh. I reset the system´s configuration by ESXi "F2 menu" for no.

I would like to debug that error. Does anybody has a hint how to do that? Is there something like a troubleshooting guide to vSphere? Which logfiles should I look up first and which configuration or logfiles could I post to get help from the community?

best regards

Martin Haneke