SSL-enabled dashboard does not play nicely with a frontend HAproxy. To fix that issue there are two new configuration options:
1. Disable redirection on standby managers. A HTTP error (500) will be returned instead of a redirection.
$ ceph config set mgr mgr/dashboard/standby_behaviour "error"
2. Configure the HTTP error status code.
$ ceph config set mgr mgr/dashboard/standby_error_status_code 503