i had this error while running zmbackup
all services seemed to be running
$ zmbackup -f -a all
Error occurred: error while proxying request to target server: HTTP/1.1 503 Service Unavailable
this is the first mailbox of 2 mailbox servers. It also supposed to run proxy but even after i ran zimbra-proxy, it is not stated by zmcontrol status output
$ zmcontrol status
$ zmnginxctl status
nginx is running.