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
- Memory usage: Be cautious with the number of metrics you track, as each unique metric consumes memory.
- 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.
- Clear interval: Use the clear_interval option to periodically reset long-term metrics and prevent unbounded growth of metric data.
- 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.
