Make sure we start system pipeline before normal pipeline

PipelineAction now have an `execution_priority`, we use this method to change the priority of a create action when we are creating a system pipeline

Fixes #6885

logstash-core/lib/logstash/config/pipeline_config.rb

@@ -23,6 +23,10 @@ module LogStash module Config
       @config_string = config_parts.collect(&:config_string).join("\n")
     end
 
+    def system?
+      @settings.get("pipeline.system")
+    end
+
     def ==(other)
       config_hash == other.config_hash && pipeline_id == other.pipeline_id
     end

logstash-core/lib/logstash/pipeline_action.rb

@@ -5,9 +5,9 @@ require "logstash/pipeline_action/stop"
 require "logstash/pipeline_action/reload"
 
 module LogStash module PipelineAction
-  ORDERING = [
-    LogStash::PipelineAction::Create,
-    LogStash::PipelineAction::Reload,
-    LogStash::PipelineAction::Stop
-  ]
+  ORDERING = {
+    LogStash::PipelineAction::Create => 100,
+    LogStash::PipelineAction::Reload => 200,
+    LogStash::PipelineAction::Stop => 300
+  }
 end end

logstash-core/lib/logstash/pipeline_action/base.rb

@@ -6,7 +6,6 @@
 # Some actions could be retryable, or have a delay or timeout.
 module LogStash module PipelineAction
   class Base
-
     # Only used for debugging purpose and in the logger statement.
     def inspect
       "#{self.class.name}/pipeline_id:#{pipeline_id}"
@@ -17,8 +16,13 @@ module LogStash module PipelineAction
       raise "`#execute` Not implemented!"
     end
 
+    # See the definition in `logstash/pipeline_action.rb` for the default ordering
+    def execution_priority
+      ORDERING.fetch(self.class)
+    end
+
     def <=>(other)
-      order = ORDERING.index(self.class) <=> ORDERING.index(other.class)
+      order = self.execution_priority <=> other.execution_priority
       order.nonzero? ? order : self.pipeline_id <=> other.pipeline_id
     end
   end

logstash-core/lib/logstash/pipeline_action/create.rb

@@ -21,6 +21,14 @@ module LogStash module PipelineAction
       @pipeline_config.pipeline_id
     end
 
+    # Make sure we execution system pipeline like the monitoring
+    # before any user defined pipelines, system pipeline register hooks into the system that will be
+    # triggered by the user defined pipeline.
+    def execution_priority
+      default_priority = super
+      @pipeline_config.system? ? default_priority * -1 : default_priority
+    end
+
     # The execute assume that the thread safety access of the pipeline
     # is managed by the caller.
     def execute(agent, pipelines)

logstash-core/spec/logstash/config/pipeline_config_spec.rb

@@ -57,4 +57,20 @@ describe LogStash::Config::PipelineConfig do
     not_same_pipeline_id = described_class.new(source, :another_pipeline, unordered_config_parts, settings)
     expect(subject).not_to eq(not_same_pipeline_id)
   end
+
+  describe "#system?" do
+    context "when the pipeline is a system pipeline" do
+      let(:settings) { mock_settings({ "pipeline.system" => true })}
+
+      it "returns true if the pipeline is a system pipeline" do
+        expect(subject.system?).to be_truthy
+      end
+    end
+
+    context "when is not a system pipeline" do
+      it "returns false if the pipeline is not a system pipeline" do
+        expect(subject.system?).to be_falsey
+      end
+    end
+  end
 end

logstash-core/spec/logstash/pipeline_action/create_spec.rb

@@ -1,6 +1,7 @@
 # encoding: utf-8
 require "spec_helper"
 require_relative "../../support/helpers"
+require_relative "../../support/matchers"
 require "logstash/pipeline_action/create"
 require "logstash/instrument/null_metric"
 require "logstash/inputs/generator"
@@ -66,4 +67,17 @@ describe LogStash::PipelineAction::Create do
       end
     end
   end
+
+  context "when sorting create action" do
+    let(:pipeline_config) { mock_pipeline_config(:main, "input { generator { id => '123' } } output { null {} }") }
+    let(:system_pipeline_config) { mock_pipeline_config(:main_2, "input { generator { id => '123' } } output { null {} }", { "pipeline.system" => true }) }
+
+    it "should give higher priority to system pipeline" do
+      action_user_pipeline = described_class.new(pipeline_config, metric)
+      action_system_pipeline = described_class.new(system_pipeline_config, metric)
+
+      sorted = [action_user_pipeline, action_system_pipeline].sort
+      expect(sorted).to eq([action_system_pipeline, action_user_pipeline])
+    end
+  end
 end

logstash-core/spec/logstash/state_resolver_spec.rb

@@ -18,6 +18,11 @@ describe LogStash::StateResolver do
     clear_data_dir
   end
 
+  after do
+    # ensure that the the created pipeline are closed
+    running_pipelines.each { |_, pipeline| pipeline.close }
+  end
+
   context "when no pipeline is running" do
     let(:running_pipelines) { {} }
 
@@ -44,12 +49,6 @@ describe LogStash::StateResolver do
     context "when a pipeline is running" do
       let(:running_pipelines) { { :main => mock_pipeline(:main) } }
 
-
-      after do
-        # ensure that the the created pipeline are closed
-        running_pipelines.each { |_, pipeline| pipeline.close }
-      end
-
       context "when the pipeline config contains a new one and the existing" do
         let(:pipeline_configs) { [mock_pipeline_config(:hello_world), mock_pipeline_config(:main)] }
 
@@ -104,6 +103,7 @@ describe LogStash::StateResolver do
         }
       end
 
+      context "without system pipeline" do
         let(:pipeline_configs) do
           [
             mock_pipeline_config(:main1),
@@ -126,5 +126,32 @@ describe LogStash::StateResolver do
           )
         end
       end
+
+      context "with system pipeline" do
+        let(:pipeline_configs) do
+          [
+            mock_pipeline_config(:main1),
+            mock_pipeline_config(:main9),
+            mock_pipeline_config(:main5, "input { generator {}}"),
+            mock_pipeline_config(:main3, "input { generator {}}"),
+            mock_pipeline_config(:main7),
+            mock_pipeline_config(:monitoring, "input { generator {}}", { "pipeline.system" => true }),
+          ]
+        end
+
+        it "creates the system pipeline before user defined pipelines" do
+          expect(subject.resolve(running_pipelines, pipeline_configs)).to have_actions(
+            [:create, :monitoring],
+            [:create, :main7],
+            [:create, :main9],
+            [:reload, :main3],
+            [:reload, :main5],
+            [:stop, :main2],
+            [:stop, :main4],
+            [:stop, :main6]
+          )
+        end
+      end
+    end
   end
 end