Logstash Elasticsearch Filter Plugin

The Elasticsearch filter plugin in Logstash allows you to enrich events with data from Elasticsearch indices. It's particularly useful when you need to add information to your events based on existing data in Elasticsearch, enabling more complex data processing and enrichment workflows.

Syntax

elasticsearch {
  hosts => ["localhost:9200"]
  index => "my_index"
  query_template => "template.json"
  fields => { "@timestamp" => "started" }
}

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

Example Use Case

Suppose you have log events with IP addresses and want to enrich them with geolocation data stored in an Elasticsearch index. Here's an example configuration:

filter {
  elasticsearch {
    hosts => ["localhost:9200"]
    index => "ip_geolocation"
    query_template => "{ \"query\": { \"term\": { \"ip\": \"%{[ip]}\" } } }"
    fields => {
      "[geoip][country_name]" => "[country]"
      "[geoip][city_name]" => "[city]"
    }
  }
}

This configuration will look up the IP address in the "ip_geolocation" index and add the corresponding country and city to the event.

Common Issues and Best Practices

1. Performance: Be mindful of the load you're putting on your Elasticsearch cluster, especially with high-volume event streams.
2. Caching: Consider using the cache_size option to improve performance for frequently queried data.
3. Error handling: Use conditional statements to handle cases where the Elasticsearch query returns no results.
4. Query optimization: Ensure your queries are efficient to avoid slowing down your Logstash pipeline.

Frequently Asked Questions

Q: Can I use multiple Elasticsearch hosts for load balancing?
A: Yes, you can specify multiple hosts in the hosts array for load balancing and failover.

Q: How can I handle errors if the Elasticsearch query fails?
A: You can use Logstash's error handling mechanisms, such as the tag_on_failure option, to mark events that failed enrichment.

Q: Is it possible to use dynamic field names in the query?
A: Yes, you can use event field values in your query by using the %{[field_name]} syntax in the query_template.

Q: Can I use this filter to update documents in Elasticsearch?
A: No, this filter is for reading data from Elasticsearch only. To update documents, you should use the Elasticsearch output plugin.

Q: How can I improve the performance of the Elasticsearch filter?
A: You can improve performance by using caching, optimizing your queries, and ensuring your Elasticsearch cluster is properly sized for the workload.