Previously docker used obsolete rfc3164 syslog format for syslog. rfc3164 explicitly
uses semicolon as a separator between 'TAG' and 'Content' section of the log message.
Docker uses semicolon as a separator between image name and version tag.
When {{.ImageName}} was used as a tag expression and contained ":" syslog parser mistreated
"tag" part of the image name as syslog message body, which resulted in incorrect "syslogtag" been reported by syslog
daemon.
Use of rfc5424 log format partually fixes the issue as it does not use semicolon as a separator.
However using default rfc5424 syslog format itroduces backward incompatability because rsyslog template keyword %syslogtag%
is parsed differently. In rfc3164 it uses the "TAG" part reported before the "pid" part. In rfc5424 it uses "appname" part reported
before the pid part, while tag part is introduced by %msgid% part.
For more information on rsyslog configuration properties see: http://www.rsyslog.com/doc/master/configuration/properties.html
Added two options to specify logging in either rfc5424, rfc3164 format or unix format omitting hostname in order to keep backwards compatability with
previous versions.
Signed-off-by: Solganik Alexander <solganik@gmail.com>
Solganik Alexander