root@mysql-master:~# grep "start_tls" /var/log/sensu/sensu-server.log 
/opt/sensu/embedded/lib/ruby/gems/2.0.0/gems/eventmachine-1.0.3/lib/em/connection.rb:411:in `block in start_tls': Could not find /etc/sensu/ssl/key.pem for start_tls (EventMachine::FileNotFoundException)
    from /opt/sensu/embedded/lib/ruby/gems/2.0.0/gems/eventmachine-1.0.3/lib/em/connection.rb:409:in `start_tls'

root@mysql-master:~# ls -l /etc/sensu/ssl/key.pem 
-rw-r--r-- 1 root root 1679 May 13 23:25 /etc/sensu/ssl/key.pem

Обожаю такие ошибки.