--- title: Ruby filter plugin description: Plugin version: v3.1.8 (Other versions), Released on: 2022-01-24, Changelog. For questions about the plugin, open a topic in the Discuss forums. For bugs... url: https://www.elastic.co/docs/reference/logstash/plugins/plugins-filters-ruby products: - Logstash applies_to: - Elastic Stack: Generally available --- # Ruby filter plugin - Plugin version: v3.1.8 ([Other versions](https://www.elastic.co/docs/reference/logstash/versioned-plugins/filter-ruby-index)) - Released on: 2022-01-24 - [Changelog](https://github.com/logstash-plugins/logstash-filter-ruby/blob/v3.1.8/CHANGELOG.md) ## Getting help For questions about the plugin, open a topic in the [Discuss](http://discuss.elastic.co) forums. For bugs or feature requests, open an issue in [Github](https://github.com/logstash-plugins/logstash-filter-ruby). For the list of Elastic supported plugins, please consult the [Elastic Support Matrix](https://www.elastic.co/support/matrix#matrix_logstash_plugins). ## Description Execute ruby code. This filter accepts inline ruby code or a ruby file. The two options are mutually exclusive and have slightly different ways of working, which are described below. This plugin’s concurrency-safety depends on your code. Be sure to read up on [how to avoid concurrency issues](#plugins-filters-ruby-concurrency). ### Inline ruby code To add inline ruby in your filter, place all code in the `code` option. This code will be executed for every event the filter receives. You can also place ruby code in the `init` option. It will be executed only once during the plugin’s register phase. For example, to cancel 90% of events, you can do this: ``` filter { ruby { # Cancel 90% of events code => "event.cancel if rand <= 0.90" } } ``` If you need to create additional events, you must use a specific syntax `new_event_block.call(event)` like in this example duplicating the input event ``` filter { ruby { code => "new_event_block.call(event.clone)" } } ``` Defining methods in the [`code` option](#plugins-filters-ruby-code) can significantly reduce throughput. Use the [`init` option](#plugins-filters-ruby-init) instead. ### Using a Ruby script file As the inline code can become complex and hard to structure inside of a text string in `code`, it’s then preferable to place the Ruby code in a .rb file, using the `path` option. ``` filter { ruby { # Cancel 90% of events path => "/etc/logstash/drop_percentage.rb" script_params => { "percentage" => 0.9 } } } ``` The ruby script file should define the following methods: - `register(params)`: An optional register method that receives the key/value hash passed in the `script_params` configuration option - `filter(event)`: A mandatory Ruby method that accepts a Logstash event and must return an array of events Below is an example implementation of the `drop_percentage.rb` ruby script that drops a configurable percentage of events: ``` # the value of `params` is the value of the hash passed to `script_params` # in the logstash configuration def register(params) @drop_percentage = params["percentage"] end # the filter method receives an event and must return a list of events. # Dropping an event means not including it in the return array, # while creating new ones only requires you to add a new instance of # LogStash::Event to the returned array def filter(event) if rand >= @drop_percentage return [event] else return [] end end ``` ### Testing the ruby script To validate the behaviour of the `filter` method you implemented, the Ruby filter plugin provides an inline test framework where you can assert expectations. The tests you define will run when the pipeline is created and will prevent it from starting if a test fails. You can also verify if the tests pass using the logstash `-t` flag. For example above, you can write at the bottom of the `drop_percentage.rb` ruby script the following test: ``` def register(params) # .. end def filter(event) # .. end test "drop percentage 100%" do parameters do { "percentage" => 1 } end in_event { { "message" => "hello" } } expect("drops the event") do |events| events.size == 0 end end ``` We can now test that the ruby script we’re using is implemented correctly: ``` % bin/logstash -e "filter { ruby { path => '/etc/logstash/drop_percentage.rb' script_params => { 'drop_percentage' => 0.5 } } }" -t [2017-10-13T13:44:29,723][INFO ][logstash.filters.ruby.script] Test run complete {:script_path=>"/etc/logstash/drop_percentage.rb", :results=>{:passed=>1, :failed=>0, :errored=>0}} Configuration OK [2017-10-13T13:44:29,887][INFO ][logstash.runner ] Using config.test_and_exit mode. Config Validation Result: OK. Exiting Logstash ``` ## Avoiding concurrency issues When events are flowing through a pipeline with multiple workers, a single shared instance of this filter may end up processing many events *simultaneously*. This means that your script needs to be written to avoid mutating shared state unless it is done in a thread-safe manner. In Ruby, the name of a variable determines its scope. The following guidance may help you avoid *accidentally* mutating shared state: - Freely use Local Variables, whose name begins with a lower-case letter or an underscore (`_`). - Local Variables are available only to the individual event being processed, and are automatically cleaned up. - Exercise caution when *modifying* Instance Variables, whose names begin with `@` followed by a lower-case letter or an underscore (`_`). - Instance Variables are shared between *all* worker threads in this pipeline, which may be processing multiple events simultaneously. - It is safe to *set* Instance Variables in a [script](#plugins-filters-ruby-using-script-file)-defined `register` function or with [`init`](#plugins-filters-ruby-init), but they should not be modified while processing events unless safe-guarded by mutual exclusion. - Instance Variables are *not* persisted across pipeline restarts or plugin crashes. - *Avoid* using variables whose scope is not limited to the plugin instance, as they can cause hard-to-debug problems that span beyond the individual plugin or pipeline: - Class Variables: begin with `@@`. - Global Variables: begin with a `$`. - Constants: begin with a capital letter. ## Ruby Filter Configuration Options This plugin supports the following configuration options plus the [Common options](#plugins-filters-ruby-common-options) described later. | Setting | Input type | Required | |----------------------------------------------------------------------------------|------------------------------------------------------------------------------|----------| | [`code`](#plugins-filters-ruby-code) | [string](/docs/reference/logstash/plugins/value-types#string) | No | | [`init`](#plugins-filters-ruby-init) | [string](/docs/reference/logstash/plugins/value-types#string) | No | | [`path`](#plugins-filters-ruby-path) | [string](/docs/reference/logstash/plugins/value-types#string) | No | | [`script_params`](#plugins-filters-ruby-script_params) | [hash](/docs/reference/logstash/plugins/value-types#hash),{} | No | | [`tag_on_exception`](#plugins-filters-ruby-tag_on_exception) | [string](/docs/reference/logstash/plugins/value-types#string),_rubyexception | No | | [`tag_with_exception_message`](#plugins-filters-ruby-tag_with_exception_message) | [boolean](/docs/reference/logstash/plugins/value-types#boolean),_false | No | Also see [Common options](#plugins-filters-ruby-common-options) for a list of options supported by all filter plugins. ### `code` - Value type is [string](/docs/reference/logstash/plugins/value-types#string) - There is no default value for this setting. - This setting cannot be used together with `path`. The code to execute for every event. You will have an `event` variable available that is the event itself. See the [Event API](https://www.elastic.co/guide/en/logstash/current/event-api.html) for more information. ### `init` - Value type is [string](/docs/reference/logstash/plugins/value-types#string) - There is no default value for this setting. Any code to execute at logstash startup-time ### `path` - Value type is [string](/docs/reference/logstash/plugins/value-types#string) - There is no default value for this setting. - This setting cannot be used together with `code`. The path of the ruby script file that implements the `filter` method. ### `script_params` - Value type is [hash](/docs/reference/logstash/plugins/value-types#hash) - Default value is `{}` A key/value hash with parameters that are passed to the register method of your ruby script file defined in `path`. ### `tag_on_exception` - Value type is [string](/docs/reference/logstash/plugins/value-types#string) - Default value is `_rubyexception` Tag to add to events in case the ruby code (either inline or file based) causes an exception. ### `tag_with_exception_message` - Value type is [boolean](/docs/reference/logstash/plugins/value-types#boolean) - Default value is `false` If `true` adds a tag to the event that is the concatenation of `tag_with_exception_message` and the exception message. ## Common options These configuration options are supported by all filter plugins: | Setting | Input type | Required | |----------------------------------------------------------|-----------------------------------------------------------------|----------| | [`add_field`](#plugins-filters-ruby-add_field) | [hash](/docs/reference/logstash/plugins/value-types#hash) | No | | [`add_tag`](#plugins-filters-ruby-add_tag) | [array](/docs/reference/logstash/plugins/value-types#array) | No | | [`enable_metric`](#plugins-filters-ruby-enable_metric) | [boolean](/docs/reference/logstash/plugins/value-types#boolean) | No | | [`id`](#plugins-filters-ruby-id) | [string](/docs/reference/logstash/plugins/value-types#string) | No | | [`periodic_flush`](#plugins-filters-ruby-periodic_flush) | [boolean](/docs/reference/logstash/plugins/value-types#boolean) | No | | [`remove_field`](#plugins-filters-ruby-remove_field) | [array](/docs/reference/logstash/plugins/value-types#array) | No | | [`remove_tag`](#plugins-filters-ruby-remove_tag) | [array](/docs/reference/logstash/plugins/value-types#array) | No | ### `add_field` - Value type is [hash](/docs/reference/logstash/plugins/value-types#hash) - Default value is `{}` If this filter is successful, add any arbitrary fields to this event. Field names can be dynamic and include parts of the event using the `%{field}`. Example: ``` filter { ruby { add_field => { "foo_%{somefield}" => "Hello world, from %{host}" } } } ``` ``` # You can also add multiple fields at once: filter { ruby { add_field => { "foo_%{somefield}" => "Hello world, from %{host}" "new_field" => "new_static_value" } } } ``` If the event has field `"somefield" == "hello"` this filter, on success, would add field `foo_hello` if it is present, with the value above and the `%{host}` piece replaced with that value from the event. The second example would also add a hardcoded field. ### `add_tag` - Value type is [array](/docs/reference/logstash/plugins/value-types#array) - Default value is `[]` If this filter is successful, add arbitrary tags to the event. Tags can be dynamic and include parts of the event using the `%{field}` syntax. Example: ``` filter { ruby { add_tag => [ "foo_%{somefield}" ] } } ``` ``` # You can also add multiple tags at once: filter { ruby { add_tag => [ "foo_%{somefield}", "taggedy_tag"] } } ``` If the event has field `"somefield" == "hello"` this filter, on success, would add a tag `foo_hello` (and the second example would of course add a `taggedy_tag` tag). ### `enable_metric` - Value type is [boolean](/docs/reference/logstash/plugins/value-types#boolean) - Default value is `true` Disable or enable metric logging for this specific plugin instance by default we record all the metrics we can, but you can disable metrics collection for a specific plugin. ### `id` - Value type is [string](/docs/reference/logstash/plugins/value-types#string) - There is no default value for this setting. Add a unique `ID` to the plugin configuration. If no ID is specified, Logstash will generate one. It is strongly recommended to set this ID in your configuration. This is particularly useful when you have two or more plugins of the same type, for example, if you have 2 ruby filters. Adding a named ID in this case will help in monitoring Logstash when using the monitoring APIs. ``` filter { ruby { id => "ABC" } } ``` ### `periodic_flush` - Value type is [boolean](/docs/reference/logstash/plugins/value-types#boolean) - Default value is `false` Call the filter flush method at regular interval. Optional. ### `remove_field` - Value type is [array](/docs/reference/logstash/plugins/value-types#array) - Default value is `[]` If this filter is successful, remove arbitrary fields from this event. Fields names can be dynamic and include parts of the event using the %{field} Example: ``` filter { ruby { remove_field => [ "foo_%{somefield}" ] } } ``` ``` # You can also remove multiple fields at once: filter { ruby { remove_field => [ "foo_%{somefield}", "my_extraneous_field" ] } } ``` If the event has field `"somefield" == "hello"` this filter, on success, would remove the field with name `foo_hello` if it is present. The second example would remove an additional, non-dynamic field. ### `remove_tag` - Value type is [array](/docs/reference/logstash/plugins/value-types#array) - Default value is `[]` If this filter is successful, remove arbitrary tags from the event. Tags can be dynamic and include parts of the event using the `%{field}` syntax. Example: ``` filter { ruby { remove_tag => [ "foo_%{somefield}" ] } } ``` ``` # You can also remove multiple tags at once: filter { ruby { remove_tag => [ "foo_%{somefield}", "sad_unwanted_tag"] } } ``` If the event has field `"somefield" == "hello"` this filter, on success, would remove the tag `foo_hello` if it is present. The second example would remove a sad, unwanted tag as well.