Logstash memcached Filter Plugin

The memcached filter plugin for Logstash allows you to interact with a Memcached server to retrieve or store data based on event fields. This plugin is particularly useful for enriching log data with additional information stored in Memcached or for caching frequently accessed data to improve performance.

Syntax

filter {
  memcached {
    hosts => ["localhost:11211"]
    get => { "key_field" => "destination_field" }
    set => { "key_field" => "value_field" }
    ttl => 3600
  }
}

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

Example Use Case

Suppose you want to enrich log events with user information stored in Memcached:

filter {
  memcached {
    hosts => ["memcached.example.com:11211"]
    get => { "user_id" => "user_info" }
    set => { "cache_key" => "event_data" }
    ttl => 1800
  }
}

In this example, the plugin retrieves user information from Memcached using the user_id field as the key and stores it in the user_info field. It also caches the entire event data using a cache_key with a TTL of 30 minutes.

Common Issues and Best Practices

1. Connection Issues: Ensure that Memcached is running and accessible from the Logstash instance.
2. Performance: Use batch operations when possible to reduce network overhead.
3. Data Consistency: Be aware of cache expiration and potential data staleness.
4. Error Handling: Implement proper error handling to manage cases where Memcached is unavailable or keys are not found.

Frequently Asked Questions

Q: Can I use multiple Memcached servers with this plugin?
A: Yes, you can specify multiple Memcached servers in the hosts configuration option for load balancing and redundancy.

Q: How does the plugin handle Memcached connection failures?
A: The plugin will log errors and continue processing events if Memcached is unavailable. It's important to monitor these logs and handle failures appropriately in your pipeline.

Q: Can I use this plugin to cache the results of expensive computations?
A: Absolutely. You can use the set option to store computed results in Memcached for faster retrieval in subsequent events.

Q: Is it possible to use Memcached as a rate limiter with this plugin?
A: While not directly supported, you can implement basic rate limiting by using Memcached to store counters with expiration times.

Q: How can I ensure that sensitive data is not cached inadvertently?
A: Carefully select which fields to cache and consider using encryption for sensitive data before storing it in Memcached.