Ruby filter plugin
editRuby filter plugin
edit- Plugin version: v3.1.7
- Released on: 2021-05-04
- Changelog
For other versions, see the Versioned plugin docs.
Installation
editFor plugins not bundled by default, it is easy to install by running bin/logstash-plugin install logstash-filter-ruby
. See Working with plugins for more details.
Getting Help
editFor questions about the plugin, open a topic in the Discuss forums. For bugs or feature requests, open an issue in Github. For the list of Elastic supported plugins, please consult the Elastic Support Matrix.
Description
editExecute 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.
Inline ruby code
editTo 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 can significantly reduce throughput. Use the init
option instead.
Using a Ruby script file
editAs 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 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 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 [] # return empty array to cancel event end end
Testing the ruby script
editTo 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
editWhen 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-defined
register
function or withinit
, 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.
-
Class Variables: begin with
Ruby Filter Configuration Options
editThis plugin supports the following configuration options plus the Common Options described later.
Also see Common Options for a list of options supported by all filter plugins.
code
edit- Value type is 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 for more information.
init
edit- Value type is string
- There is no default value for this setting.
Any code to execute at logstash startup-time
path
edit- Value type is 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.
Common Options
editThe following configuration options are supported by all filter plugins:
Setting | Input type | Required |
---|---|---|
No |
||
No |
||
No |
||
No |
||
No |
||
No |
||
No |
add_field
edit- Value type is 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
edit- Value type is 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
edit- Value type is 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
edit- Value type is 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
edit- Value type is boolean
-
Default value is
false
Call the filter flush method at regular interval. Optional.
remove_field
edit- Value type is 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
edit- Value type is 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.