Use typhoeus adapter for Elasticsearch client

We get Faraday connection issues because the client
is unable to keep the connection open. Adding the
typhoeus adapter will allow our Elastic client to have
a "keep-alive" connection, as that is not included by
default.

Gemfile

@@ -149,6 +149,7 @@ gem 'aws-sdk-core', '~> 3'
 gem 'aws-sdk-cloudformation', '~> 1'
 gem 'aws-sdk-s3', '~> 1'
 gem 'faraday_middleware-aws-sigv4', '~>0.3.0'
+gem 'typhoeus', '~> 1.4.0' # Used with Elasticsearch to support http keep-alive connections
 
 # Markdown and HTML processing
 gem 'html-pipeline', '~> 2.13.2'

Gemfile.lock

@@ -333,6 +333,8 @@ GEM
     escape_utils (1.2.1)
     et-orbi (1.2.1)
       tzinfo
+    ethon (0.15.0)
+      ffi (>= 1.15.0)
     eventmachine (1.2.7)
     excon (0.71.1)
     execjs (2.8.1)
@@ -1311,6 +1313,8 @@ GEM
       tty-screen (~> 0.8)
       wisper (~> 2.0)
     tty-screen (0.8.1)
+    typhoeus (1.4.0)
+      ethon (>= 0.9.0)
     tzinfo (2.0.4)
       concurrent-ruby (~> 1.0)
     u2f (0.2.1)
@@ -1655,6 +1659,7 @@ DEPENDENCIES
   timecop (~> 0.9.1)
   toml-rb (~> 2.0)
   truncato (~> 0.7.11)
+  typhoeus (~> 1.4.0)
   u2f (~> 0.2.1)
   undercover (~> 0.4.4)
   unf (~> 0.1.4)

config/feature_flags/development/use_typhoeus_elasticsearch_adapter.yml

+---
+name: use_typhoeus_elasticsearch_adapter
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/76879
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/348607
+milestone: '14.7'
+type: development
+group: group::global search
+default_enabled: false

ee/lib/gem_extensions/elasticsearch/model/client.rb

@@ -15,16 +15,19 @@ module GemExtensions
 
         cattr_accessor :cached_client
         cattr_accessor :cached_config
+        cattr_accessor :cached_adapter
 
         def client(_client = nil)
           store = ::GemExtensions::Elasticsearch::Model::Client
 
           store::CLIENT_MUTEX.synchronize do
-            config = Gitlab::CurrentSettings.elasticsearch_config
+            config = ::Gitlab::CurrentSettings.elasticsearch_config
+            adapter = ::Gitlab::Elastic::Client.adapter
 
-            if store.cached_client.nil? || config != store.cached_config
+            if store.cached_client.nil? || config != store.cached_config || adapter != store.cached_adapter
               store.cached_client = ::Gitlab::Elastic::Client.build(config)
               store.cached_config = config
+              store.cached_adapter = adapter
             end
           end
 

ee/lib/gitlab/elastic/client.rb

@@ -14,6 +14,7 @@ module Gitlab
       # and configures itself based on those parameters
       def self.build(config)
         base_config = {
+          adapter: self.adapter,
           urls: config[:url],
           transport_options: {
             request: {
@@ -37,6 +38,10 @@ module Gitlab
         end
       end
 
+      def self.adapter
+        ::Feature.enabled?(:use_typhoeus_elasticsearch_adapter) ? :typhoeus : :net_http
+      end
+
       def self.resolve_aws_credentials(config)
         # Resolve credentials in order
         # 1.  Static config

ee/spec/lib/gitlab/elastic/client_spec.rb

@@ -23,6 +23,37 @@ RSpec.describe Gitlab::Elastic::Client do
         expect(options).to include(open_timeout: described_class::OPEN_TIMEOUT, timeout: nil)
       end
 
+      context 'with typhoeus adapter for keep-alive connections' do
+        it 'sets typhoeus as the adapter' do
+          options = client.transport.options
+
+          expect(options).to include(adapter: :typhoeus)
+        end
+
+        context 'when use_typhoeus_elasticsearch_adapter FeatureFlag is disabled' do
+          before do
+            stub_feature_flags(use_typhoeus_elasticsearch_adapter: false)
+          end
+
+          it 'uses the net/http adapter' do
+            options = client.transport.options
+            expect(options).to include(adapter: :net_http)
+          end
+        end
+
+        context 'cached client when FeatureFlag changes' do
+          it 'successfully changes adapter from net/http to typhoeus' do
+            stub_feature_flags(use_typhoeus_elasticsearch_adapter: false)
+            adapter = Issue.__elasticsearch__.client.transport.connections.first.connection.builder.adapter
+            expect(adapter).to eq(::Faraday::Adapter::NetHttp)
+
+            stub_feature_flags(use_typhoeus_elasticsearch_adapter: true)
+            adapter = Issue.__elasticsearch__.client.transport.connections.first.connection.builder.adapter
+            expect(adapter).to eq(::Faraday::Adapter::Typhoeus)
+          end
+        end
+      end
+
       context 'with client_request_timeout in config' do
         let(:params) { { url: 'http://dummy-elastic:9200', client_request_timeout: 30 } }