Plesk interface runs slow: cURL cannot communicate with license server

Symptoms

• Plesk interface is unresponsive or Plesk shows the message that the license key is expired

• The following error is shown in Plesk and in /var/log/plesk/panel.log file:

  ERR [1] Token validation failed: Can not connect to 'ka.plesk.com' (6:6). Please check connection to 'ka.plesk.com' or contact Plesk support: <a href='https://www.plesk.com/support/' target='_blank'>https://www.plesk.com/support/</a>.; ; KV network error (ka.plesk.com: cURL cannot communicate with license server https://ka.plesk.com/jsonrest/pkp/20/verify-key (): Couldn't resolve host name(6)

• Retrieving the license from CLI fails with one of the following messages:

  # plesk bin license --retrieve
  Updating Plesk license key:
  [2017-11-24 05:18:02] ERR [panel] KeyUpdate Result code: 2 Unspecified error
  [2017-11-24 05:18:02] ERR [panel] KeyUpdate Result desc: License key is not prolongated yet

  ---

  # plesk bin license --retrieve
  Updating Plesk license key:
  2018-09-02T21:25:04+01:00 ERR (3): KeyUpdate Result code: 2 Network failure
  2018-09-02T21:25:04+01:00 ERR (3): KeyUpdate Result desc: Couldn't resolve host name

• Telnet connection to ka.plesk.com works correctly:

  # telnet ka.plesk.com
  Trying 195.214.233.80...
  Connected to ka.plesk.com.
  Escape character is '^]'.

• The next command is executed correctly (Do not mind the error):

  # curl https://ka.plesk.com/jsonrest/pkp/20/verify-key
  Authorization failed

• DNS records of ka.plesk.com cannot be resolved against some of the configured nameservers:

  # cat /etc/resolv.conf
  nameserver 203.0.112.2
  nameserver 8.8.8.8
  # dig ka.plesk.com @203.0.112.2
  ...
  ;; connection timed out; no servers could be reached

Cause

DNS server misconfiguration.

Resolution

1. Resolve the issue on the side of the DNS server or remove the misconfigured DNS server from the interface settings

2. Connect to the server via SSH and reinstall license key manually:

   # plesk bin license --install A00000-A00000-A00000-A00000-A00000