Description* UPDATE: server restarted successfully and Address Book issue has been resolved. *
We received an error with the Lync Address Book service that will require an immediate restart of the Front-End Server 1 for Lync. Since users are load balanced across all 4 servers, only users connected to server 1 will experience a brief outage where you will be moved to another available server. All existing conversations will still continue and should be seamless for the most part.
Server 1 will be back up in about 10-15 minutes.