Unable to resolve host ip-XX: Resource temporarily unavailable

Since this morning, on my EC2 Ubuntu, I 'm not able to sudo update/upgrade or launch mysql service and have the following error Unable to resolve host ip-XX: Resource temporarily unavailable.
The IP in the message error is not the Server's IP (Elastic IP).
Everythings was working last week...

Is someone know this issue ?

Error example with mysql start :

• sudo /etc/init.d/mysql start
  sudo: unable to resolve host ip-XX: Resource temporarily unavailable
  [....] Starting mysql (via systemctl): mysql.serviceJob for mariadb.service failed because the control process exited with error code.
  See "systemctl status mariadb.service" and "journalctl -xe" for details.
  failed!