The monitoring() source allows you to select which statistics of syslog-ng PE you want to monitor. In addition, the statistics are available as structured name-value pairs, so you can format the output similarly to other log messages. That way, you can easily convert the statistics and metrics, for example, into JSON or WELF format. That way, you can send the statistics of your log messages into a monitoring solution, for example, into Riemann, Redis, or Graphite.

The monitoring() source queries the statistics (counters) that syslog-ng PE collects, formats them, and optionally resets the counters. The monitoring() source emits only these messages, making it easy to route them to their appropriate destination. The stats-level() global option determines exactly which statistics syslog-ng PE collects.

Declaration
source s_monitor{
  monitoring(
    query("*")
  );
};
Example: Save all statistics into a file in JSON format

The following configuration increases the stats-level() option to 3, and generates a JSON-formatted message every 10 seconds. The generated message contains every available statistics, and is saved into the /var/log/syslog-ng-statistics.log file.

@version: 7.0 
options { 
  stats-level(3); 
  keep-hostname(no); 
}; 

source s_monitor { monitoring( 
    query("*") 
    freq(1) 
    message-template("$(format-flat-json --scope nv_pairs)") 
  ); 
}; 
				
destination d_file { 
  file("/var/log/syslog-ng-statistics.log"); 
}; 
				
log { 
  source(s_monitor); 
  destination(d_file); 
};

The generated message is similar to this one:

[2021-09-02T13:30:18.003557] Outgoing message; message='Sep 2 13:30:18 test-host syslog-ng[71345]: {"tag..source.s_monitor.processed":"111","src.severity.7.processed":"0","src.severity.6.processed":"111","src.severity.5.processed":"0","src.severity.4.processed":"0","src.severity.3.processed":"0","src.severity.2.processed":"0","src.severity.1.processed":"0","src.severity.0.processed":"0","src.sender.s_monitor#0.test-host.stamp":"1630582216","src.sender.s_monitor#0.test-host.processed":"111","src.sender.test-host.stamp":"1630582216","src.sender.test-host.processed":"111","src.program.syslog-ng.stamp":"1630582216","src.program.syslog-ng.processed":"111","src.monitoring.s_monitor#0.stamp":"1630582216","src.monitoring.s_monitor#0.processed":"111","src.host.s_monitor#0.test-host.stamp":"1630582216","src.host.s_monitor#0.test-host.processed":"111","src.host.test-host.stamp":"1630582216","src.host.test-host.processed":"111","src.facility.other.pr'

For reference, the JSON part in a readable format is:

{ "tag..source.s_monitor.processed": "111", "src.severity.7.processed": "0", "src.severity.6.processed": "111", "src.severity.5.processed": "0", "src.severity.4.processed": "0", "src.severity.3.processed": "0", "src.severity.2.processed": "0", "src.severity.1.processed": "0", "src.severity.0.processed": "0", "src.sender.s_monitor#0.test-host.stamp": "1630582216", "src.sender.s_monitor#0.test-host.processed": "111", "src.sender.test-host.stamp": "1630582216", "src.sender.test-host.processed": "111", "src.program.syslog-ng.stamp": "1630582216", "src.program.syslog-ng.processed": "111", "src.monitoring.s_monitor#0.stamp": "1630582216", "src.monitoring.s_monitor#0.processed": "111", "src.host.s_monitor#0.test-host.stamp": "1630582216", "src.host.s_monitor#0.test-host.processed": "111", "src.host.test-host.stamp": "1630582216", "src.host.test-host.processed": "111", "src.facility.other.processed": "0", "src.facility.9.processed": "0", "src.facility.8.processed": "0", "src.facility.7.processed": "0", "src.facility.6.processed": "0", "src.facility.5.processed": "111", "src.facility.4.processed": "0", "src.facility.3.processed": "0", "src.facility.23.processed": "0", "src.facility.22.processed": "0", "src.facility.21.processed": "0", "src.facility.20.processed": "0", "src.facility.2.processed": "0", "src.facility.19.processed": "0", "src.facility.18.processed": "0", "src.facility.17.processed": "0", "src.facility.16.processed": "0", "src.facility.15.processed": "0", "src.facility.14.processed": "0", "src.facility.13.processed": "0", "src.facility.12.processed": "0", "src.facility.11.processed": "0", "src.facility.10.processed": "0", "src.facility.1.processed": "0", "src.facility.0.processed": "0", "source.s_monitor.processed": "111", "global.sdata_updates.processed": "0", "global.scratch_buffers_count.queued": "280", "global.scratch_buffers_bytes.queued": "50944", "global.payload_reallocs.processed": "557", "global.msg_clones.processed": "0", "global.msg_allocated_bytes.value": "1056", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.written": "111", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.truncated_count": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.truncated_bytes": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.queued": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.processed": "111", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.msg_size_max": "3019", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.msg_size_avg": "2991", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.memory_usage": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.eps_since_start": "1", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.eps_last_24h": "1", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.eps_last_1h": "1", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.dropped": "0", "destination.d_file.processed": "111", "center.received.processed": "111", "center.queued.processed": "111", "PROGRAM": "syslog-ng", "PID": "71345" }