Plesk upgrade or update failed: Failed to connect to autoinstall.plesk.com port 80: Connection refused

Symptoms

Following errors appear during Plesk upgrade or update:

CONFIG_TEXT: ERROR: Upgrade step InstallExtCatalog.php failed with code 1 and output: ERROR: PleskUserException: Execution of /opt/psa/admin/plib/modules/catalog/scripts/post-install.php failed with exit code 1 and the output:
ERR [extension/catalog] Failed to connect to ext.plesk.com port 443: Connection refused (Package.php:583)

CONFIG_TEXT: Error: error during prepare patch plesk-17.8.11~patch6 Failed to download the file http://autoinstall.plesk.com/PSA_17.8.11/microupdates/MU5/dist-deb-Ubuntu-16.04-x86_64/react-sortable-hoc.plesk-ui-library.min.js.map Failed to connect to autoinstall.plesk.com port 80: Connection refused

Cause

Firewall rules restrict outbound connection to autoinstall.plesk.com or autoinstall-win.plesk.com via 80 port and/or to ext.plesk.com via 443 port.

Resolution

Configure Firewall rules on the server to allow connection to autoinstall.plesk.com:80, autoinstall-win.plesk.com:80 or ext.plesk.com:443. 

Additional information

How to manage ports for Plesk on Linux Server