Logstash metrics Filter Plugin

The metrics filter plugin in Logstash is used for aggregating metrics from events. It allows you to calculate various statistical measures like count, mean, min, max, and percentiles over a specified time window. This plugin is particularly useful for monitoring and analyzing numerical data in your log events.

Syntax

metrics {
  meter => { "event_name" => "metric_name" }
  timer => { "event_name" => "metric_name" }
  gauge => { "event_name" => "metric_name" }
  counter => { "event_name" => "metric_name" }
  flush_interval => 60
  clear_interval => 3600
}

For detailed configuration options, refer to the official Logstash metrics filter plugin documentation.

Example Use Case

Suppose you want to monitor the response times of a web application. You can use the metrics filter to calculate average response time and request count over a 5-minute interval:

filter {
  metrics {
    meter => { "http.request" => "requests" }
    timer => { "http.response_time" => "response_time" }
    flush_interval => 300
    add_tag => "metrics"
  }
}

This configuration will generate events with aggregated metrics every 5 minutes, including the total request count and average response time.

Common Issues and Best Practices

  1. Memory usage: Be cautious with the number of metrics you track, as each unique metric consumes memory.
  2. Flush interval: Choose an appropriate flush_interval based on your needs. Too short intervals may impact performance, while too long intervals may delay metric updates.
  3. Clear interval: Use the clear_interval option to periodically reset long-term metrics and prevent unbounded growth of metric data.
  4. Tagging: Add a tag to metric events for easy identification and routing in your Logstash pipeline.

Frequently Asked Questions

Q: How does the metrics filter differ from the aggregate filter?
A: The metrics filter is specifically designed for numerical aggregations and statistical calculations, while the aggregate filter is more general-purpose and can work with non-numerical data as well.

Q: Can I use the metrics filter to calculate percentiles?
A: Yes, you can use the percentiles parameter in the timer configuration to calculate specific percentiles of your metrics.

Q: How often are the metrics flushed?
A: Metrics are flushed based on the flush_interval parameter. By default, it's set to 5 minutes (300 seconds).

Q: Can I reset metrics after a certain period?
A: Yes, you can use the clear_interval parameter to reset metrics periodically. This is useful for long-running Logstash instances to prevent unbounded growth of metric data.

Q: How can I ensure that metric events don't interfere with my regular log processing?
A: It's a good practice to add a specific tag to metric events (using add_tag) and then use that tag in your output configuration to route metric events separately from regular log events.

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