These days we patched the vCenter nodes to 41000 and one of them failed to login after the update.
The update process was finished successfully while after the reboot when I tried to login it through the VMware Appliance Management page I always got 'Unable to login' prompt and nothing happened.
I waited for several minutes and even I could login the updated vCenter to manage ESXi hosts and VMs, I still could not login the management page on port 5480. I made sure the password was correct so I guessed something was wrong after the update.
Google is always a great helper and I found below web page:Solved: Unable to log into vCenter 6.7 VMware Appliance Management page
I got the same error in the log /opt/vmware/var/log/lighttpd/error.log:
2018-09-30 14:31:46: (/build/mts/release/bora-7927448/studio/src/vami/apps/lighttpd/1.4.45/src/mod_proxy.c.1417) proxy - re-enabled: 127.0.0.1 8201 2018-09-30 14:31:48: (/build/mts/release/bora-7927448/studio/src/vami/apps/lighttpd/1.4.45/src/mod_proxy.c.1041) establishing connection failed: Connection refused 2018-09-30 14:31:48: (/build/mts/release/bora-7927448/studio/src/vami/apps/lighttpd/1.4.45/src/mod_proxy.c.1153) proxy-server disabled: 127.0.0.1 8201 13 2018-09-30 14:31:48: (/build/mts/release/bora-7927448/studio/src/vami/apps/lighttpd/1.4.45/src/mod_proxy.c.523) no proxy-handler found for: /rest/appliance/system/version 2018-09-30 14:31:53: (/build/mts/release/bora-7927448/studio/src/vami/apps/lighttpd/1.4.45/src/mod_proxy.c.1417) proxy - re-enabled: 127.0.0.1 8201
With command 'service-control --status' I found the service applmgmt was stopped so I started it then I could login the management page.
It was weird that this service was configured to start automatically so I will update this post when I find the the reason why it was not started as expected.