Nginx is enabled on server.
allow rule for
System policy for incoming traffic in Plesk > Tools & Settings > Security > Firewall websites become unavailable.
The following error can be found in website's error log:
2015/10/08 21:41:55 [error] 8481#0: *3227 upstream timed out (110: Connection timed out) while connecting to upstream, client: 10.20.30.40, server: domain.tld, request: "GET /webpage.html HTTP/1.1", upstream: "https://10.20.30.40:7081/webpage.html", host: "domain.tld"
Software issue #PPP-2289 . It will be fixed in future product updates.
Create allow rules for ports 7080, 7081 in Plesk > Tools & Settings > Security > Firewall > Modify Plesk Firewall rules > Add Сustom Rule