• Plugin version: v3.1.8
• Released on: 2022-01-24
• Changelog

For other versions, see theVersioned plugin docs.

For questions about the plugin, open a topic in theDiscuss forums. For bugs or feature requests, open an issue inGithub. For the list of Elastic supported plugins, please consult theElastic Support Matrix.

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.

To add inline ruby in your filter, place all code in thecode option. This code will be executed for every event the filter receives. You can also place ruby code in theinit 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 syntaxnew_event_block.call(event) like in this example duplicating the input event

filter {  ruby {    code => "new_event_block.call(event.clone)"  }}

As the inline code can become complex and hard to structure inside of a text string incode, it’s then preferable to place the Ruby code in a .rb file, using thepath 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 thescript_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 thedrop_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 configurationdef 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 arraydef filter(event)if rand >= @drop_percentagereturn [event]elsereturn []endend

1. return empty array to cancel event

To validate the behaviour of thefilter 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 thedrop_percentage.rb ruby script the following test:

def register(params)  # ..enddef filter(event)  # ..endtest "drop percentage 100%" do  parameters do    { "percentage" => 1 }  end  in_event { { "message" => "hello" } }  expect("drops the event") do |events|    events.size == 0  endend

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

When events are flowing through a pipeline with multiple workers, a single shared instance of this filter may end up processing many eventssimultaneously. 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 avoidaccidentally 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 whenmodifying Instance Variables, whose names begin with@ followed by a lower-case letter or an underscore (_).

  • Instance Variables are shared betweenall worker threads in this pipeline, which may be processing multiple events simultaneously.
  • It is safe toset Instance Variables in ascript-definedregister function or withinit, but they should not be modified while processing events unless safe-guarded by mutual exclusion.
  • Instance Variables arenot 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.

This plugin supports the following configuration options plus theCommon options described later.

Also seeCommon options for a list of options supported by all filter plugins.

• Value type isstring
• There is no default value for this setting.
• This setting cannot be used together withpath.

The code to execute for every event. You will have anevent variable available that is the event itself. See theEvent API for more information.

• Value type isstring
• There is no default value for this setting.

Any code to execute at logstash startup-time

• Value type isstring
• There is no default value for this setting.
• This setting cannot be used together withcode.

The path of the ruby script file that implements thefilter method.

• Value type ishash
• Default value is{}

A key/value hash with parameters that are passed to the register method of your ruby script file defined inpath.

• Value type isstring
• Default value is_rubyexception

Tag to add to events in case the ruby code (either inline or file based) causes an exception.

• Value type isboolean
• Default value isfalse

Iftrue adds a tag to the event that is the concatenation oftag_with_exception_message and the exception message.

These configuration options are supported by all filter plugins:

• Value type ishash
• 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 fieldfoo_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.

• Value type isarray
• 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 tagfoo_hello (and the second example would of course add ataggedy_tag tag).

• Value type isboolean
• Default value istrue

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.

• Value type isstring
• There is no default value for this setting.

Add a uniqueID 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"  }}

• Value type isboolean
• Default value isfalse

Call the filter flush method at regular interval. Optional.

• Value type isarray
• 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 namefoo_hello if it is present. The second example would remove an additional, non-dynamic field.

• Value type isarray
• 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 tagfoo_hello if it is present. The second example would remove a sad, unwanted tag as well.