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Description

The log_mon probe tails a log file, counting newly-appended lines matching includePattern (and not matching excludePattern). It tracks a byte offset between runs — only counts new lines, resets on truncation/rotation.

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Config fields

FieldTypeRequiredDefaultDescription
typestringYes—Must be "log_mon"
filePathstringYes—Log file path to scan
includePatternstringYes—Regex for lines to count
excludePatternstringNo—Regex to exclude lines that matched include
maxAgeSecondsint64No—Skip scan if file hasn’t changed within this many seconds
readFromEndboolNotruetrue: start from EOF on first run. false: start from beginning

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Metrics

MetricTypeDescription
vms.log_mon.match_countgaugeNumber of matching lines in this run

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Example config

{
  "type": "log_mon",
  "filePath": "/var/log/app/app.log",
  "includePattern": "ERROR|FATAL",
  "excludePattern": "healthcheck",
  "maxAgeSeconds": 300
}

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Notes

  • Reads up to 8 MiB per run. Remainder is picked up on the next tick.
  • Only counts complete lines (ending with \n).
  • File truncation (size drops below offset) resets to offset 0.