Logstash Filter Plugin: Redis Lookup

This is a custom Logstash filter plugin that enriches event data by querying a Redis datastore. The plugin retrieves values from Redis using a field in the event as the lookup key and supports various Redis data types (string, hash, list, set, zset).

It is fully free and open source under the Apache 2.0 License.

🔧 Features

• Look up values from Redis based on a specified event field
• Supports all Redis data types: string, hash, list, set, and zset
• Optional fallback value if the key is not found or Redis is unreachable
• Configurable key source field, destination field, and override behavior
• Wildcard pattern matching against Redis-stored patterns
• Efficient SCAN-based pattern lookup for large datasets
• Regex pattern caching for improved performance
• Array value support with append option
• Automatic JSON parsing for string values
• Configurable connection timeout and Redis database selection

📄 Configuration Options

Setting	Description	Default
host	Redis host address	"127.0.0.1"
port	Redis port	6379
password	Redis password (optional)	nil
db	Redis database number	0
field	Event field to use as lookup key	(required)
destination	Field where to store lookup results	"redis"
override	Overwrite destination field if it exists	false
fallback	Default value if lookup fails	nil
timeout	Redis connection timeout in seconds	5
append	Append results to an array instead of overwriting	false
pattern_matching	Enable wildcard pattern matching	false
pattern_namespace	Redis key namespace for patterns	""
scan_count	Number of items to scan per iteration	1000

🛠 Configuration Examples

Standard Lookup

filter {
  redis {
    host => "localhost"
    port => 6379
    db => 0
    field => "user_id"
    destination => "user_data"
    override => true
    fallback => "unknown"
  }
}

Pattern Matching with Namespace

filter {
  redis {
    field => "[source][ip]"
    destination => "[threat][match]"
    pattern_matching => true
    pattern_namespace => "ip_patterns:"
    scan_count => 2000
  }
}

Appending Multiple Values

filter {
  redis {
    field => "tags"
    destination => "enriched_data"
    append => true
    fallback => {"default" => "value"}
  }
}

🧠 How It Works

Value Lookup Modes

1. Direct Lookup: Uses the field value as a direct Redis key
2. Pattern Matching: When enabled, scans Redis for pattern keys that match the field value

Data Type Handling

• Strings: Stored directly or parsed as JSON if valid
• Hashes: Converted to nested objects
• Lists/Sets: Converted to arrays
• Sorted Sets: Converted to arrays with scores

Pattern Matching Output

When pattern matching finds a result, the output includes metadata:

{
  "matched_pattern": "192.168.*",
  "value": "internal_network",
  "original_value": "192.168.1.1"
}

Array Handling with append

When append is true, multiple matches will be collected in an array:

{
  "enriched_data": [
    {"matched_pattern": "192.168.*", "value": "internal"},
    {"matched_pattern": "192.*", "value": "private"}
  ]
}

Need Help?

Need help? Try #logstash on freenode IRC or the https://discuss.elastic.co/c/logstash discussion forum.

Developing

1. Plugin Developement and Testing

Code

• To get started, you'll need JRuby with the Bundler gem installed.

• Create a new plugin or clone and existing from the GitHub logstash-plugins organization. We also provide example plugins.

• Install dependencies

bundle install

Test

• Update your dependencies

bundle install

• Run tests

bundle exec rspec

2. Running your unpublished Plugin in Logstash

2.1 Run in a local Logstash clone

• Edit Logstash Gemfile and add the local plugin path, for example:

gem "logstash-filter-awesome", :path => "/your/local/logstash-filter-awesome"

• Install plugin

# Logstash 2.3 and higher
bin/logstash-plugin install --no-verify

# Prior to Logstash 2.3
bin/plugin install --no-verify

• Run Logstash with your plugin

bin/logstash -e 'filter {awesome {}}'

At this point any modifications to the plugin code will be applied to this local Logstash setup. After modifying the plugin, simply rerun Logstash.

2.2 Run in an installed Logstash

You can use the same 2.1 method to run your plugin in an installed Logstash by editing its Gemfile and pointing the :path to your local plugin development directory or you can build the gem and install it using:

• Build your plugin gem

gem build logstash-filter-awesome.gemspec

• Install the plugin from the Logstash home

# Logstash 2.3 and higher
bin/logstash-plugin install --no-verify

# Prior to Logstash 2.3
bin/plugin install --no-verify

• Start Logstash and proceed to test the plugin

Contributing

All contributions are welcome: ideas, patches, documentation, bug reports, complaints, and even something you drew up on a napkin.

Programming is not a required skill. Whatever you've seen about open source and maintainers or community members saying "send patches or die" - you will not see that here.

It is more important to the community that you are able to contribute.

For more information about contributing, see the CONTRIBUTING file.