nixos/modules/syslog/default.nix

{ ... }:
{
  services.rsyslogd = {
    enable = true;
    defaultConfig = ''
      *.*  action(type="omfwd" target="10.7.89.108" port="514" protocol="udp"
                  action.resumeRetryCount="100"
                  queue.type="linkedList" queue.size="10000")
    '';
  };
  systemd.services.syslog.after = [ "network-online.target" ];
}