snmptrapd logging to rsyslogd and snmptrapd.log with logrotate rotation on Ubuntu

etc_logrotate.d_snmptrapd

# snmptrapd.log files as per `systemctl edit snmptrapd.service`
# (in addition to logging traps to syslog)
/var/log/snmptrapd.log
{
  rotate 7
  daily
  missingok
  notifempty
  delaycompress
  compress
  postrotate
    /usr/bin/systemctl restart snmptrapd.service
  endscript
}

etc_snmp_snmptrapd.conf

authCommunity log public
disableAuthorization yes

systemctl-edit-snmptrapd.service

[Service]
ExecStart=
# log to syslog daemon facility and append to snmptrapd.log
ExecStart=/usr/sbin/snmptrapd -n -f -A -Lf /var/log/snmptrapd.log -Lsd
#
# n.b. set these options via `systemctl edit snmptrapd.service`, NOT via /etc/defaults/snmptrapd, which is ignored
#
# n.b. option "-LSwd" (uppercase 'S' -LS<level><facility> for syslog w/level + facility)
#      which is proivded as example does NOT work.
#      You MUST use the facility-only syslog option e.g. -Lsd (lowercase 's' -Ls<facility>)
#
# Options:
#   -n no reverse DNS lookups on IPs
#   -f don't fork
#   -A append to logfile, don't overwrite
#   -a ignore authenticationFailure traps
#   -M MIB dirlist
#   -m MIB module list
#   -t DISABLE logging traps to syslog (runs hook scripts only)
#   -Lf log to file
#   -Ls<level><facility> log to syslog