2.3.2. Relay mode The syslog-ng Premium Edition 7 Administrator Guide
In relay mode, syslog-ng receives logs through the network from syslog-ng clients and forwards them to the central syslog-ng server using a network connection. Relays also log the messages from the relay host into a local file, or forward these messages to the central syslog-ng server.
You cannot use the following destinations in relay mode:
file() destination works only for local messages that are generated on the relay.
No license file is required to run syslog-ng in relay mode.