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
- Ensure that your start and end events have matching unique ID fields.
- Be mindful of the
timeoutsetting to prevent memory issues with unpaired events. - Use the
new_timestamp_fieldoption to store the calculated duration in a specific field. - Consider using the
timestamp_fieldoption 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.
