Logstash elapsed Filter Plugin

The elapsed filter plugin in Logstash is used to measure the time elapsed between pairs of events that share a unique ID field. This plugin is particularly useful for tracking the duration of processes, requests, or any paired events in your log data.

Syntax

elapsed {
  start_tag => "start_event"
  end_tag => "end_event"
  unique_id_field => "id"
  timeout => 30
}

For more detailed information, refer to the official Logstash elapsed filter plugin documentation.

Example Use Case and Usage

A common use case for the elapsed filter is measuring the duration of HTTP requests. Here's an example configuration:

filter {
  elapsed {
    start_tag => "start"
    end_tag => "end"
    unique_id_field => "request_id"
    new_timestamp_field => "request_duration"
  }
}

In this example, the plugin looks for events with matching request_id fields, one tagged as "start" and another as "end". It then calculates the time difference and adds it to the "end" event in the request_duration field.

Common Issues and Best Practices

  1. Ensure that your start and end events have matching unique ID fields.
  2. Be mindful of the timeout setting to prevent memory issues with unpaired events.
  3. Use the new_timestamp_field option to store the calculated duration in a specific field.
  4. Consider using the timestamp_field option if your events don't use the default @timestamp field.

Frequently Asked Questions

Q: Can the elapsed filter handle out-of-order events?
A: Yes, the elapsed filter can handle out-of-order events as long as they share the same unique ID and have the correct start and end tags.

Q: What happens if an end event arrives but there's no corresponding start event?
A: In this case, the end event will pass through the filter unchanged, and no elapsed time will be calculated.

Q: Is there a limit to how many unique IDs the elapsed filter can track simultaneously?
A: There's no hard limit, but tracking too many unique IDs can lead to increased memory usage. Use the timeout setting to manage this.

Q: Can I use the elapsed filter to measure time across multiple Logstash instances?
A: It's challenging to use the elapsed filter across multiple Logstash instances as it relies on in-memory state. For distributed scenarios, consider using a centralized storage solution.

Q: How does the elapsed filter handle events with the same unique ID but multiple start or end tags?
A: The elapsed filter will use the first start event and the first end event it encounters for a given unique ID. Subsequent events with the same ID and tag will be ignored for timing purposes.

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