Fix Logstash pipelines management in case of slow loading pipelines or disabled webserver (#12571)

This commit avoid an error in gathering monitoring information when webserver is disabled or is not yet started;
which could happen with slow loading pipelines or no pipelines defined from the central management UI.

(cherry picked from commit 91996cf2a2)

logstash-core/lib/logstash/agent.rb

@@ -121,10 +121,10 @@ class LogStash::Agent
 
     transition_to_running
 
-    converge_state_and_update
-
     start_webserver_if_enabled
 
+    converge_state_and_update
+
     if auto_reload?
       # `sleep_then_run` instead of firing the interval right away
       Stud.interval(@reload_interval, :sleep_then_run => true) do

x-pack/lib/monitoring/inputs/metrics/stats_event_factory.rb

@@ -12,6 +12,7 @@ module LogStash; module Inputs; class Metrics;
       @snapshot = snapshot
       @metric_store = @snapshot.metric_store
       @cluster_uuid = cluster_uuid
+      @webserver_enabled = LogStash::SETTINGS.get_value("http.enabled")
     end
 
     def make(agent, extended_performance_collection=true, collection_interval=10)
@@ -124,8 +125,13 @@ module LogStash; module Inputs; class Metrics;
     end
 
     def fetch_node_stats(agent, stats)
+      if @webserver_enabled
+        http_addr = stats.get_shallow(:http_address).value
+      else
+        http_addr = nil
+      end
       @global_stats.merge({
-        "http_address" => stats.get_shallow(:http_address).value,
+        "http_address" => http_addr,
         "ephemeral_id" => agent.ephemeral_id
       })
     end

x-pack/spec/monitoring/inputs/metrics/stats_event_factory_spec.rb

@@ -6,6 +6,37 @@ require "monitoring/inputs/metrics/stats_event_factory"
 require "logstash/config/pipeline_config"
 require 'json'
 
+shared_examples_for("old model monitoring event with webserver setting") do
+  let(:schema_file) { File.join(schemas_path, "monitoring_document_schema.json") }
+
+  it "should be valid" do
+    global_stats = {"uuid" => "00001" }
+    sut = described_class.new(global_stats, collector.snapshot_metric, nil)
+    LogStash::SETTINGS.set_value("monitoring.enabled", false)
+    LogStash::SETTINGS.set_value("http.enabled", webserver_enabled)
+
+    monitoring_evt = sut.make(agent, true)
+    json = JSON.parse(monitoring_evt.to_json)
+    expect(JSON::Validator.fully_validate(schema_file, monitoring_evt.to_json)).to be_empty
+  end
+end
+
+shared_examples_for("new model monitoring event with webserver setting") do
+  let(:schema_file) { File.join(schemas_path, "monitoring_document_new_schema.json") }
+
+  it "should be valid" do
+    global_stats = {"uuid" => "00001" }
+    sut = described_class.new(global_stats, collector.snapshot_metric, "funky_cluster_uuid")
+    LogStash::SETTINGS.set_value("monitoring.enabled", true)
+    LogStash::SETTINGS.set_value("http.enabled", webserver_enabled)
+
+    monitoring_evt = sut.make(agent, true)
+    json = JSON.parse(monitoring_evt.to_json)
+    expect(json['type']).to eq('logstash_stats')
+    expect(JSON::Validator.fully_validate(schema_file, monitoring_evt.to_json)).to be_empty
+  end
+end
+
 describe LogStash::Inputs::Metrics::StatsEventFactory do
   let(:schemas_path) { File.join(File.dirname(__FILE__), "..", "..", "..", "..", "spec", "monitoring", "schemas") }
   let(:queue) { Concurrent::Array.new }
@@ -52,31 +83,20 @@ describe LogStash::Inputs::Metrics::StatsEventFactory do
   end
 
  context "new model" do
-   let(:schema_file) { File.join(schemas_path, "monitoring_document_new_schema.json") }
-
-   it "should be valid" do
-     global_stats = {"uuid" => "00001" }
-     sut = described_class.new(global_stats, collector.snapshot_metric, "funky_cluster_uuid")
-     LogStash::SETTINGS.set_value("monitoring.enabled", true)
-
-     monitoring_evt = sut.make(agent, true)
-     json = JSON.parse(monitoring_evt.to_json)
-     expect(json['type']).to eq('logstash_stats')
-     expect(JSON::Validator.fully_validate(schema_file, monitoring_evt.to_json)).to be_empty
+   it_behaves_like("new model monitoring event with webserver setting") do
+     let(:webserver_enabled) {false}
+   end
+   it_behaves_like("new model monitoring event with webserver setting") do
+     let(:webserver_enabled) {true}
    end
  end
 
  context "old model" do
-   let(:schema_file) { File.join(schemas_path, "monitoring_document_schema.json") }
-
-   it "should be valid" do
-     global_stats = {"uuid" => "00001" }
-     sut = described_class.new(global_stats, collector.snapshot_metric, nil)
-     LogStash::SETTINGS.set_value("monitoring.enabled", false)
-
-     monitoring_evt = sut.make(agent, true)
-     json = JSON.parse(monitoring_evt.to_json)
-     expect(JSON::Validator.fully_validate(schema_file, monitoring_evt.to_json)).to be_empty
-   end
+    it_behaves_like("old model monitoring event with webserver setting") do
+      let(:webserver_enabled) {false}
+    end
+    it_behaves_like("old model monitoring event with webserver setting") do
+      let(:webserver_enabled) {true}
+    end
   end
 end

x-pack/spec/monitoring/schemas/monitoring_document_schema.json

@@ -71,7 +71,7 @@
       "type": "object",
       "required": ["http_address", "uuid", "ephemeral_id"],
       "properties": {
-        "http_address": { "type": "string" },
+        "http_address": { "type": ["string", "null"] },
         "uuid": { "type": "string" },
         "ephemeral_id": { "type": "string" }
       }