To develop a new filter for Logstash, build a self-contained Ruby gem whose source code lives in its own GitHub repository. The Ruby gem can then be hosted and shared on RubyGems.org. You can use the example filter implementation as a starting point. (If you’re unfamiliar with Ruby, you can find an excellent quickstart guide at https://www.ruby-lang.org/en/documentation/quickstart/.)
Let’s step through creating a filter plugin using the example filter plugin.
Each Logstash plugin lives in its own GitHub repository. To create a new repository for your plugin:
- Log in to GitHub.
- Click the Repositories tab. You’ll see a list of other repositories you’ve forked or contributed to.
- Click the green New button in the upper right.
-
Specify the following settings for your new repo:
-
Repository name — a unique name of the form
logstash-filter-pluginname
. - Public or Private — your choice, but the repository must be Public if you want to submit it as an official plugin.
- Initialize this repository with a README — enables you to immediately clone the repository to your computer.
-
Repository name — a unique name of the form
- Click Create Repository.
You can create your own Logstash plugin in seconds! The generate
subcommand of bin/logstash-plugin
creates the foundation
for a new Logstash plugin with templatized files. It creates the correct directory structure, gemspec files, and dependencies so you
can start adding custom code to process data with Logstash.
For more information, see Generating plugins
Alternatively, you can use the examples repo we host on github.com
-
Clone your plugin. Replace
GITUSERNAME
with your github username, andMYPLUGINNAME
with your plugin name.-
git clone https://github.com/GITUSERNAME/logstash-
filter-MYPLUGINNAME.git
-
alternately, via ssh:
git clone [email protected]:GITUSERNAME/logstash
-filter-MYPLUGINNAME.git
-
alternately, via ssh:
-
cd logstash-filter-MYPLUGINNAME
-
-
Clone the filter plugin example and copy it to your plugin branch.
You don’t want to include the example .git directory or its contents, so delete it before you copy the example.
-
cd /tmp
-
git clone https://github.com/logstash-plugins/logstash
-filter-example.git
-
cd logstash-filter-example
-
rm -rf .git
-
cp -R * /path/to/logstash-filter-mypluginname/
-
-
Rename the following files to match the name of your plugin.
-
logstash-filter-example.gemspec
-
example.rb
-
example_spec.rb
cd /path/to/logstash-filter-mypluginname mv logstash-filter-example.gemspec logstash-filter-mypluginname.gemspec mv lib/logstash/filters/example.rb lib/logstash/filters/mypluginname.rb mv spec/filters/example_spec.rb spec/filters/mypluginname_spec.rb
-
Your file structure should look like this:
$ tree logstash-filter-mypluginname ├── Gemfile ├── LICENSE ├── README.md ├── Rakefile ├── lib │ └── logstash │ └── filters │ └── mypluginname.rb ├── logstash-filter-mypluginname.gemspec └── spec └── filters └── mypluginname_spec.rb
For more information about the Ruby gem file structure and an excellent walkthrough of the Ruby gem creation process, see http://timelessrepo.com/making-ruby-gems
Before we dive into the details, open up the plugin file in your favorite text editor and take a look.
require "logstash/filters/base" require "logstash/namespace" # Add any asciidoc formatted documentation here # This example filter will replace the contents of the default # message field with whatever you specify in the configuration. # # It is only intended to be used as an example. class LogStash::Filters::Example < LogStash::Filters::Base # Setting the config_name here is required. This is how you # configure this filter from your Logstash config. # # filter { # example { message => "My message..." } # } config_name "example" # Replace the message with this value. config :message, :validate => :string, :default => "Hello World!" public def register # Add instance variables end # def register public def filter(event) if @message # Replace the event message with our message as configured in the # config file. event.set("message", @message) end # filter_matched should go in the last line of our successful code filter_matched(event) end # def filter end # class LogStash::Filters::Example
Now let’s take a line-by-line look at the example plugin.
Logstash filter plugins require parent classes defined in
logstash/filters/base
and logstash/namespace:
require "logstash/filters/base" require "logstash/namespace"
Of course, the plugin you build may depend on other code, or even gems. Just put them here along with these Logstash dependencies.
Let’s go through the various elements of the plugin itself.
The filter plugin class should be a subclass of
LogStash::Filters::Base
:
class LogStash::Filters::Example < LogStash::Filters::Base
The class name should closely mirror the plugin name, for example:
LogStash::Filters::Example
config :variable_name, :validate => :variable_type, :default => "Default value", :required => boolean, :deprecated => boolean, :obsolete => string
The configuration, or config
section allows you to define as many (or as few)
parameters as are needed to enable Logstash to process events.
There are several configuration attributes:
-
:validate
- allows you to enforce passing a particular data type to Logstash for this configuration option, such as:string
,:password
,:boolean
,:number
,:array
,:hash
,:path
(a file-system path),uri
,:codec
(since 1.2.0),:bytes
. Note that this also works as a coercion in that if I specify "true" for boolean (even though technically a string), it will become a valid boolean in the config. This coercion works for the:number
type as well where "1.2" becomes a float and "22" is an integer. -
:default
- lets you specify a default value for a parameter -
:required
- whether or not this parameter is mandatory (a Booleantrue
or -
:list
- whether or not this value should be a list of values. Will typecheck the list members, and convert scalars to one element lists. Note that this mostly obviates the array type, though if you need lists of complex objects that will be more suitable.false
) -
:deprecated
- informational (also a Booleantrue
orfalse
) -
:obsolete
- used to declare that a given setting has been removed and is no longer functioning. The idea is to provide an informed upgrade path to users who are still using a now-removed setting.
Logstash filters must implement the register
and filter
methods.
public def register end # def register
The Logstash register
method is like an initialize
method. It was originally
created to enforce having super
called, preventing headaches for newbies.
(Note: It may go away in favor of initialize
, in conjunction with some
enforced testing to ensure super
is called.)
public
means the method can be called anywhere, not just within the class.
This is the default behavior for methods in Ruby, but it is specified explicitly
here anyway.
You can also assign instance variables here (variables prepended by @
).
Configuration variables are now in scope as instance variables, like @message
public def filter(event) if @message # Replace the event message with our message as configured in the # config file. event.set("message", @message) end # filter_matched should go in the last line of our successful code filter_matched(event) end # def filter
The plugin’s filter
method is where the actual filtering work takes place!
Inside the filter
method you can refer to the event data using the Event
object. Event is the main object that encapsulates data flow internally in Logstash
and provides an API for the plugin developers to interact with the
event’s content.
The filter
method should also handle any event dependent configuration by
explicitly calling the sprintf
method available in Event class. For example:
field_foo = event.sprintf(field)
Note that configuration variables are now in scope as instance variables, like
@message
filter_matched(event)
Calling the filter_matched
method upon successful execution of the plugin will
ensure that any fields or tags added through the Logstash configuration for this
filter will be handled correctly. For example, any add_field
, remove_field
,
add_tag
and/or remove_tag
actions will be performed at this time.
Event methods such as event.cancel
are now available to control the workflow
of the event being processed.
At this point in the process you have coded your plugin and are ready to build a Ruby Gem from it. The following information will help you complete the process.
A require
statement in Ruby is used to include necessary code. In some cases
your plugin may require additional files. For example, the collectd plugin
uses
the types.db
file provided by collectd. In the main directory of your plugin,
a file called vendor.json
is where these files are described.
The vendor.json
file contains an array of JSON objects, each describing a file
dependency. This example comes from the
collectd
codec plugin:
[{ "sha1": "a90fe6cc53b76b7bdd56dc57950d90787cb9c96e", "url": "http://collectd.org/files/collectd-5.4.0.tar.gz", "files": [ "/src/types.db" ] }]
-
sha1
is the sha1 signature used to verify the integrity of the file referenced byurl
. -
url
is the address from where Logstash will download the file. -
files
is an optional array of files to extract from the downloaded file. Note that while tar archives can use absolute or relative paths, treat them as absolute in this array. Iffiles
is not present, all files will be uncompressed and extracted into the vendor directory.
Another example of the vendor.json
file is the
geoip
filter
The process used to download these dependencies is to call rake vendor
. This
will be discussed further in the testing section of this document.
Another kind of external dependency is on jar files. This will be described
in the "Add a gemspec
file" section.
As a plugin evolves, an option or feature may no longer serve the intended purpose, and the developer may want to deprecate its usage. Deprecation warns users about the option’s status, so they aren’t caught by surprise when it is removed in a later release.
Logstash 7.6 introduced a deprecation logger to make handling those situations easier. You can use the adapter to ensure that your plugin can use the deprecation logger while still supporting older versions of Logstash. See the readme for more information and for instructions on using the adapter.
Deprecations are noted in the logstash-deprecation.log
file in the
log
directory.
Gemfiles allow Ruby’s Bundler to maintain the dependencies for your plugin. Currently, all we’ll need is the Logstash gem, for testing, but if you require other gems, you should add them in here.
See Bundler’s Gemfile page for more details.
source 'https://rubygems.org' gemspec gem "logstash", :github => "elastic/logstash", :branch => "7.17"
Gemspecs define the Ruby gem which will be built and contain your plugin.
More information can be found on the Rubygems Specification page.
Gem::Specification.new do |s| s.name = 'logstash-filter-example' s.version = '0.1.0' s.licenses = ['Apache License (2.0)'] s.summary = "This filter does x, y, z in Logstash" s.description = "This gem is a logstash plugin required to be installed on top of the Logstash core pipeline using $LS_HOME/bin/logstash-plugin install gemname. This gem is not a stand-alone program" s.authors = ["Elastic"] s.email = '[email protected]' s.homepage = "http://www.elastic.co/guide/en/logstash/current/index.html" s.require_paths = ["lib"] # Files s.files = Dir['lib/**/*','spec/**/*','vendor/**/*','*.gemspec','*.md','CONTRIBUTORS','Gemfile','LICENSE','NOTICE.TXT'] # Tests s.test_files = s.files.grep(%r{^(test|spec|features)/}) # Special flag to let us know this is actually a logstash plugin s.metadata = { "logstash_plugin" => "true", "logstash_group" => "filter" } # Gem dependencies s.add_runtime_dependency "logstash-core-plugin-api", ">= 1.60", "<= 2.99" s.add_development_dependency 'logstash-devutils' end
It is appropriate to change these values to fit your plugin. In particular,
s.name
and s.summary
should reflect your plugin’s name and behavior.
s.licenses
and s.version
are also important and will come into play when
you are ready to publish your plugin.
Logstash and all its plugins are licensed under Apache License, version 2 ("ALv2"). If you make your plugin publicly available via RubyGems.org, please make sure to have this line in your gemspec:
-
s.licenses = ['Apache License (2.0)']
The gem version, designated by s.version
, helps track changes to plugins over
time. You should use semver versioning strategy for version numbers.
At the bottom of the gemspec
file is a section with a comment:
Gem dependencies
. This is where any other needed gems must be mentioned. If
a gem is necessary for your plugin to function, it is a runtime dependency. If
a gem are only used for testing, then it would be a development dependency.
You can also have versioning requirements for your dependencies—including other Logstash plugins:
# Gem dependencies s.add_runtime_dependency "logstash-core-plugin-api", ">= 1.60", "<= 2.99" s.add_development_dependency 'logstash-devutils'
This gemspec has a runtime dependency on the logstash-core-plugin-api and requires that it have a version number greater than or equal to version 1.60 and less than or equal to version 2.99.
All plugins have a runtime dependency on the logstash-core-plugin-api
gem, and
a development dependency on logstash-devutils
.
In some cases, such as the Elasticsearch output plugin, your code may depend on a jar file. In cases such as this, the dependency is added in the gemspec file in this manner:
# Jar dependencies s.requirements << "jar 'org.elasticsearch:elasticsearch', '5.0.0'" s.add_runtime_dependency 'jar-dependencies'
With these both defined, the install process will search for the required jar file at http://mvnrepository.com and download the specified version.
Documentation is an important part of your plugin. All plugin documentation is rendered and placed in the Logstash Reference and the Versioned plugin docs.
See Document your plugin for tips and guidelines.
Logstash loves tests. Lots of tests. If you’re using your new filter plugin in a production environment, you’ll want to have some tests to ensure you are not breaking any existing functionality.
A full exposition on RSpec is outside the scope of this document. Learn more about RSpec at http://rspec.info
For help learning about tests and testing, look in the
spec/filters/
directory of several other similar
plugins.
Now let’s start with a fresh clone of the plugin, build it and run the tests.
-
Clone your plugin into a temporary location Replace
GITUSERNAME
with your github username, andMYPLUGINNAME
with your plugin name.-
git clone https://github.com/GITUSERNAME/logstash-
filter-MYPLUGINNAME.git
-
alternately, via ssh:
git clone [email protected]:GITUSERNAME/logstash-
filter-MYPLUGINNAME.git
-
alternately, via ssh:
-
cd logstash-filter-MYPLUGINNAME
-
Then, you’ll need to install your plugins dependencies with bundler:
bundle install
If your plugin has an external file dependency described in vendor.json
, you
must download that dependency before running or testing. You can do this by
running:
rake vendor
And finally, run the tests:
bundle exec rspec
You should see a success message, which looks something like this:
Finished in 0.034 seconds 1 example, 0 failures
Hooray! You’re almost there! (Unless you saw failures… you should fix those first).
Now you’re ready to build your (well-tested) plugin into a Ruby gem.
You already have all the necessary ingredients, so let’s go ahead and run the build command:
gem build logstash-filter-example.gemspec
That’s it! Your gem should be built and be in the same path with the name
logstash-filter-mypluginname-0.1.0.gem
The s.version
number from your gemspec file will provide the gem version, in
this case, 0.1.0
.
You should test install your plugin into a clean installation of Logstash. Download the latest version from the Logstash downloads page.
-
Untar and cd in to the directory:
curl -O https://download.elastic.co/logstash/logstash/logstash-7.17.26.tar.gz tar xzvf logstash-7.17.26.tar.gz cd logstash-7.17.26
-
Using the plugin tool, we can install the gem we just built.
-
Replace
/my/logstash/plugins
with the correct path to the gem for your environment, and0.1.0
with the correct version number from the gemspec file.bin/logstash-plugin install /my/logstash/plugins/logstash-filter-example/logstash-filter-example-0.1.0.gem
-
After running this, you should see feedback from Logstash that it was successfully installed:
validating /my/logstash/plugins/logstash-filter-example/logstash-filter-example-0.1.0.gem >= 0 Valid logstash plugin. Continuing... Successfully installed 'logstash-filter-example' with version '0.1.0'
You can also use the Logstash plugin tool to determine which plugins are currently available:
bin/logstash-plugin list
Depending on what you have installed, you might see a short or long list of plugins: inputs, codecs, filters and outputs.
-
-
Now try running Logstash with a simple configuration passed in via the command-line, using the
-e
flag.Your results will depend on what your filter plugin is designed to do.
bin/logstash -e 'input { stdin{} } filter { example {} } output {stdout { codec => rubydebug }}'
Test your filter by sending input through stdin
and output (after filtering)
through stdout
with the rubydebug
codec, which enhances readability.
In the case of the example filter plugin, any text you send will be
replaced by the contents of the message
configuration parameter, the default
value being "Hello World!":
Testing 1, 2, 3 { "message" => "Hello World!", "@version" => "1", "@timestamp" => "2015-01-27T19:17:18.932Z", "host" => "cadenza" }
Feel free to experiment and test this by changing the message
parameter:
bin/logstash -e 'input { stdin{} } filter { example { message => "This is a new message!"} } output {stdout { codec => rubydebug }}'
Congratulations! You’ve built, deployed and successfully run a Logstash filter.
Submitting your plugin to RubyGems.org and logstash-plugins
Logstash uses RubyGems.org as its repository for all plugin artifacts. Once you have developed your new plugin, you can make it available to Logstash users by simply publishing it to RubyGems.org.
Logstash and all its plugins are licensed under Apache License, version 2 ("ALv2"). If you make your plugin publicly available via RubyGems.org, please make sure to have this line in your gemspec:
-
s.licenses = ['Apache License (2.0)']
Publishing to RubyGems.org
To begin, you’ll need an account on RubyGems.org
After creating an account,
obtain an API
key from RubyGems.org. By default, RubyGems uses the file ~/.gem/credentials
to store your API key. These credentials will be used to publish the gem.
Replace username
and password
with the credentials you created at
RubyGems.org:
curl -u username:password https://rubygems.org/api/v1/api_key.yaml > ~/.gem/credentials chmod 0600 ~/.gem/credentials
Before proceeding, make sure you have the right version in your gemspec file and commit your changes.
-
s.version = '0.1.0'
To publish version 0.1.0 of your new logstash gem:
bundle install bundle exec rake vendor bundle exec rspec bundle exec rake publish_gem
Executing rake publish_gem
:
-
Reads the version from the gemspec file (
s.version = '0.1.0'
) - Checks in your local repository if a tag exists for that version. If the tag already exists, it aborts the process. Otherwise, it creates a new version tag in your local repository.
- Builds the gem
- Publishes the gem to RubyGems.org
That’s it! Your plugin is published! Logstash users can now install your plugin by running:
bin/logstash-plugin install logstash-filter-mypluginname
Contributing your source code to logstash-plugins
It is not required to contribute your source code to logstash-plugins github organization, but we always welcome new plugins!
Some of the many benefits of having your plugin in the logstash-plugins repository are:
- Discovery. Your plugin will appear in the Logstash Reference, where Logstash users look first for plugins and documentation.
- Documentation. Your plugin documentation will automatically be added to the Logstash Reference.
- Testing. With our testing infrastructure, your plugin will be continuously tested against current and future releases of Logstash. As a result, users will have the assurance that if incompatibilities arise, they will be quickly discovered and corrected.
- Code Review. Your plugin must be reviewed by members of the community for coherence, quality, readability, stability and security.
- Tests. Your plugin must contain tests to be accepted. These tests are also subject to code review for scope and completeness. It’s ok if you don’t know how to write tests — we will guide you. We are working on publishing a guide to creating tests for Logstash which will make it easier. In the meantime, you can refer to http://betterspecs.org/ for examples.
To begin migrating your plugin to logstash-plugins, simply create a new issue in the Logstash repository. When the acceptance guidelines are completed, we will facilitate the move to the logstash-plugins organization using the recommended github process.