Plesk websites are inaccessible with proxy mode enabled: failed (111: Connection refused)

Symptoms

• One of the following errors show up in the web browser if Proxy Mode is enabled for a website:

  CONFIG_TEXT: 504 Gateway Timeout error

  CONFIG_TEXT: 502 Bad gateway

• The following error show up in /var/log/httpd/error_log:

  CONFIG_TEXT: upstream timed out (110: Connection timed out) while reading response header from upstream

  CONFIG_TEXT: AH00072: make_sock: could not bind to address 127.0.0.1:7080

• The following errors show up in /var/www/vhosts/example.com/logs/proxy_error_log:

  CONFIG_TEXT: connect() failed (111: Connection refused) while connecting to upstream, client: 203.0.113.2, server: example.com, request: "GET / HTTP/2.0", upstream: "https://127.0.0.1:7081/", host: "example.com"

Cause

Connection to ports 7080 and 7081 is blocked.

Resolution

Warning: Managing firewall rules is considered an administrative task that should be performed by the server administrator. If ports are still blocked after applying the steps on this article, It is highly possible a 3rd party application is blocking them.

Install and enable Plesk Firewall extension as explained here.

Note: When Plesk Firewall extension is installed and enabled, it opens all necessary ports for Plesk to works correctly.