We are still using the legacy config format for rsyslog in https://github.com/vyos/vyos-1x/blob/bb4611544ff73a979f927a7a1c8ea3dd1c56fb48/data/templates/rsyslog/rsyslog.conf.j2

It has been superseded by a new format:

https://www.rsyslog.com/doc/configuration/converting_to_new_format.html

There are some associated issues. For example, we use $markMessagePeriod for set system syslog global marker interval, which sends mark messages unconditionally. New rsyslog versions support sending mark messages only if there are no real messages, the old directive is now listed as obsolete (https://www.rsyslog.com/doc/configuration/input_directives/rsconf1_markmessageperiod.html) and its replacement seems to be only available in the advanced format.

• Drop file CLI option to log to dedicated files.
• Drop user CLI option to always log to user terminal - should be an op-mode command instead
• Rename host <ipv4|ipv6|fqdn> -> remote <ipv4|ipv6|fqdn>
• Add new source-address option for outgoing connections under remote source-address <ipv4|ipv6|fqdn>
• VRF can be defined per remote as remote vrf <name>
• Move global preserve-fqdn -> preserve-fqdn - move up one CLI level
• Move global marker interval -> marker interval - move up one CLI level
• Rename global -> local as every facility configured under global is actually logged locally to /var/log/messages