Since logback is using internet sockets, you have to make sure your syslog facility accepts them. Modern Linux distributions are using the rsyslog daemon for syslogging. Ensure that the configuration for internet domain sockets is enabled, either by editing/etc/rsyslog.confand uncommenting:
# Provides UDP syslog reception $ModLoad imudp $UDPServerRun 514 # Provides TCP syslog reception $ModLoad imtcp $InputTCPServerRun 514
or placing it in a file under/etc/rsyslog.dending in .conf.
Restart rsyslog.
service rsyslog restart