Conductor traffic passes through httpd+mod_proxy before reaching conductor itself (conductor runs via thin). During upgrade (or running aeolus-restart-services), conductor is restarted. The conductor init script will return successfully before thin has fully loaded the conductor app. Accessing conductor during this brief window will result in an HTTP/503 status code (Temporarily Unavailable). The default behavior of httpd/mod_proxy is to mark a backend worker as disabled for 60 seconds if the backend is determined to be unavailable; once the worker is marked as such, mod_proxy will not attempt to pass any traffic to the backend until the retry period expires. Therefor, if a user attempt to access conductor immediately after it starts, but before it has loaded completely, the user will receive an HTTP/503 error for approximately 60 seconds until the mod_proxy retry interval expires and httpd starts forwarding requests to conductor again.