Extensions Catalog in Plesk is not accessible: Failed connect to ext.plesk.com:443; No route to host

Symptoms

• The Extensions menu is not available and fails with:

  Internal server error

• The following error in logged to the file /var/log/plesk/panel.log:

  ERR [extension/catalog] Failed connect to ext.plesk.com:443; No route to host

• A manual connection attempt to ext.plesk.com from CLI fails:

  # curl -vvv https://ext.plesk.com
  * About to connect() to ext.plesk.com port 443 (#0)
  * Trying 195.181.175.6...
  * No route to host
  * Failed connect to ext.plesk.com:443; No route to host
  * Closing connection 0
  curl: (7) Failed connect to ext.plesk.com:443; No route to host

• The host ext.plesk.com resolves a different IP address(s) from the one on the curl error above:

  # host ext.plesk.com
  ext.plesk.com is an alias for 1648825949.rsc.cdn77.org.
  1648825949.rsc.cdn77.org has address 89.187.164.8

Cause

A record in /etc/hosts force the resolution of ext.plesk.com to an old or wrong IP address.

Resolution

1. Connect to the server using SSH.

2. Edit the /etc/hosts file.

3. Comment out the line(s) contaiting ext.plesk.com by adding a preceding # at the beginning of it, e.g.:

   #195.181.175.6 ext.plesk.com