Add a Plugin#id that return an ID for a plugin

This method return an ID for the plugins and be configured by the users
in the configuration like this:

```
elasticsearch {
  id => "ABC"
  ...
}
```

This information will be used when collecting metrics for a specific
plugin. Allowing the user to change it allow to stick between restart.

Fixes #3892

Fixes #4525

logstash-core/lib/logstash/filter_delegator.rb

@@ -20,7 +20,7 @@ def initialize(logger, klass, metric, *args)
       @filter = klass.new(options)
 
       # Scope the metrics to the plugin
-      @metric = metric.namespace(@filter.identifier_name)
+      @metric = metric.namespace(@filter.id.to_sym)
       @filter.metric = @metric
 
       define_flush_method if @filter.respond_to?(:flush)

logstash-core/lib/logstash/output_delegator.rb

@@ -17,12 +17,12 @@ def initialize(logger, klass, default_worker_count, metric, *args)
     @threadsafe = klass.threadsafe?
     @config = args.reduce({}, :merge)
     @klass = klass
-    
+
     # Create an instance of the input so we can fetch the identifier
     output = @klass.new(*args)
-    
+
     # Scope the metrics to the plugin
-    @metric = metric.namespace(output.identifier_name)
+    @metric = metric.namespace(output.id.to_sym)
 
     # We define this as an array regardless of threadsafety
     # to make reporting simpler, even though a threadsafe plugin will just have

logstash-core/lib/logstash/plugin.rb

@@ -5,7 +5,7 @@
 require "logstash/instrument/null_metric"
 require "cabin"
 require "concurrent"
-require "digest/md5"
+require "securerandom"
 
 class LogStash::Plugin
 
@@ -21,13 +21,19 @@ class LogStash::Plugin
   # for a specific plugin.
   config :enable_metric, :validate => :boolean, :default => true
 
-  # Under which name you want to collect metric for this plugin?
-  # This will allow you to compare the performance of the configuration change, this
-  # name need to be unique per plugin configuration.
+  # Add a unique `ID` to the plugin instance, this `ID` is used for tracking
+  # information for a specific configuration of the plugin.
+  #
+  # ```
+  # output {
+  #  stdout {
+  #    id => "ABC"
+  #  }
+  # }
+  # ```
   #
   # If you don't explicitely set this variable Logstash will generate a unique name.
-  # This name will be valid until the configuration change.
-  config :metric_identifier, :validate => :string, :default => ""
+  config :id, :validate => :string, :default => ""
 
   public
   def hash
@@ -46,6 +52,16 @@ def initialize(params=nil)
     @logger = Cabin::Channel.get(LogStash)
   end
 
+  # Return a uniq ID for this plugin configuration, by default
+  # we will generate a UUID
+  #
+  # If the user defines a `id => 'ABC'` in the configuration we will return
+  #
+  # @return [String] A plugin ID
+  def id
+    (@params["id"].nil? || @params["id"].empty?) ? SecureRandom.uuid : @params["id"]
+  end
+
   # close is called during shutdown, after the plugin worker
   # main task terminates
   public
@@ -83,21 +99,13 @@ def debug_info
   end
 
   def metric=(new_metric)
-    @metric = new_metric.namespace(identifier_name)
+    @metric = new_metric.namespace(@id)
   end
 
   def metric
     @metric_plugin ||= enable_metric ? @metric : LogStash::Instrument::NullMetric.new
   end
 
-  def identifier_name
-    @identifier_name ||= (@metric_identifier.nil? || @metric_identifier.empty?) ? "#{self.class.config_name}-#{params_hash_code}".to_sym : @identifier.to_sym
-  end
-
-  def params_hash_code
-    Digest::MD5.hexdigest(params.to_s)
-  end
-
   # Look up a plugin by type and name.
   public
   def self.lookup(type, name)
@@ -120,7 +128,6 @@ def self.lookup(type, name)
   end
 
   private
-
   # lookup a plugin by type and name in the existing LogStash module namespace
   # ex.: namespace_lookup("filter", "grok") looks for LogStash::Filters::Grok
   # @param type [String] plugin type, "input", "ouput", "filter"

logstash-core/spec/logstash/output_delegator_spec.rb

@@ -20,7 +20,7 @@
       allow(out_inst).to receive(:register)
       allow(out_inst).to receive(:multi_receive)
       allow(out_inst).to receive(:metric=).with(any_args)
-      allow(out_inst).to receive(:identifier_name).and_return("a-simple-plugin")
+      allow(out_inst).to receive(:id).and_return("a-simple-plugin")
       allow(logger).to receive(:debug).with(any_args)
     end
 
@@ -60,7 +60,7 @@
           allow(out_klass).to receive(:threadsafe?).and_return(false)
           allow(out_klass).to receive(:workers_not_supported?).and_return(false)
           allow(out_inst).to receive(:metric=).with(any_args)
-          allow(out_inst).to receive(:identifier_name).and_return("a-simple-plugin")
+          allow(out_inst).to receive(:id).and_return("a-simple-plugin")
         end
 
         it "should instantiate multiple workers" do
@@ -77,7 +77,7 @@
         before do
           allow(out_klass).to receive(:threadsafe?).and_return(true)
           allow(out_inst).to receive(:metric=).with(any_args)
-          allow(out_inst).to receive(:identifier_name).and_return("a-simple-plugin")
+          allow(out_inst).to receive(:id).and_return("a-simple-plugin")
           allow(out_klass).to receive(:workers_not_supported?).and_return(false)
         end
 

logstash-core/spec/logstash/plugin_spec.rb

@@ -1,6 +1,10 @@
 # encoding: utf-8
 require "spec_helper"
 require "logstash/plugin"
+require "logstash/outputs/base"
+require "logstash/codecs/base"
+require "logstash/inputs/base"
+require "logstash/filters/base"
 
 describe LogStash::Plugin do
   it "should fail lookup on inexisting type" do
@@ -149,4 +153,56 @@ class LogStash::Filters::Stromae < LogStash::Filters::Base
       end
     end
   end
+
+  describe "#id" do
+    plugin_types = [
+                    LogStash::Filters::Base,
+                    LogStash::Codecs::Base,
+                    LogStash::Outputs::Base,
+                    LogStash::Inputs::Base
+                  ]
+
+    plugin_types.each do |plugin_type|
+      let(:plugin) do
+        Class.new(plugin_type) do
+          config_name "simple_plugin"
+
+          config :host, :validate => :string
+          config :export, :validte => :boolean
+
+          def register; end
+        end
+      end
+
+      let(:config) do
+        {
+          "host" => "127.0.0.1",
+          "export" => true
+        }
+      end
+
+      subject { plugin.new(config) }
+
+      context "plugin type is #{plugin_type}" do
+        context "when there is not ID configured for the output" do
+          it "it uses a UUID to identify this plugins" do
+            expect(subject.id).not_to eq(nil)
+          end
+
+          it "will be different between instance of plugins" do
+            expect(subject.id).not_to eq(plugin.new(config).id)
+          end
+        end
+
+        context "When a user provide an ID for the plugin" do
+          let(:id) { "ABC" }
+          let(:config) { super.merge("id" => id) }
+
+          it "uses the user provided ID" do
+            expect(subject.id).to eq(id)
+          end
+        end
+      end
+    end
+  end
 end