Plesk is slow: cURL cannot communicate with license server

Symptoms

• Plesk is unresponsive and may say the license is expired

• Plesk shows the following error

  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 on the command line fails with one of these messages

  ERR [panel] KeyUpdate Result code: 2 Unspecified error
  ERR [panel] KeyUpdate Result desc: License key is not prolongated yet

  ERR (3): KeyUpdate Result code: 2 Network failure
  ERR (3): KeyUpdate Result desc: Couldn't resolve host name

• ka.plesk.com can't be resolved by some of the serves' DNS resolvers:

  # dig ka.plesk.com @203.0.112.2
  ...
  ;; connection timed out; no servers could be reached

Cause

DNS server misconfiguration.

Resolution

1. Resolve the DNS server issue with the hosting provider, or change the system's DNS resolvers

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

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