Add `connection_specification_name/db_config` to `LB::Configuration`

This is in preparation to allow asynchronous handling of replicas
and re-use of primary connection in a load balancing context.

lib/gitlab/database/load_balancing/configuration.rb

@@ -5,9 +5,11 @@ module Gitlab
     module LoadBalancing
       # Configuration settings for a single LoadBalancer instance.
       class Configuration
+        attr_reader :connection_specification_name, :connection_db_config
+
         attr_accessor :hosts, :max_replication_difference,
                       :max_replication_lag_time, :replica_check_interval,
-                      :service_discovery, :model
+                      :service_discovery
 
         # Creates a configuration object for the given ActiveRecord model.
         def self.for_model(model)
@@ -45,6 +47,8 @@ module Gitlab
         end
 
         def initialize(model, hosts = [])
+          @connection_specification_name = model.connection_specification_name
+          @connection_db_config = model.connection_db_config
           @max_replication_difference = 8.megabytes
           @max_replication_lag_time = 60.0
           @replica_check_interval = 60.0

lib/gitlab/database/load_balancing/load_balancer.rb

@@ -27,7 +27,7 @@ module Gitlab
               HostList.new(configuration.hosts.map { |addr| Host.new(addr, self) })
             end
 
-          @name = @configuration.model.connection_db_config.name.to_sym
+          @name = @configuration.connection_db_config.name.to_sym
         end
 
         def primary_only?
@@ -252,7 +252,7 @@ module Gitlab
         # leverage that.
         def pool
           ActiveRecord::Base.connection_handler.retrieve_connection_pool(
-            @configuration.model.connection_specification_name,
+            @configuration.connection_specification_name,
             role: ActiveRecord::Base.writing_role,
             shard: ActiveRecord::Base.default_shard
           ) || raise(::ActiveRecord::ConnectionNotEstablished)

lib/gitlab/database/load_balancing/setup.rb

@@ -42,7 +42,7 @@ module Gitlab
           @model.class_attribute(:sticking)
 
           @model.connection = ConnectionProxy.new(lb)
-          @model.sticking = Sticking.new(lb)
+          @model.sticking = Sticking.new(lb, @model)
         end
 
         def setup_service_discovery

lib/gitlab/database/load_balancing/sticking.rb

@@ -10,9 +10,9 @@ module Gitlab
         # the primary.
         EXPIRATION = 30
 
-        def initialize(load_balancer)
+        def initialize(load_balancer, model)
           @load_balancer = load_balancer
-          @model = load_balancer.configuration.model
+          @model = model
         end
 
         # Unsticks or continues sticking the current request.

spec/lib/gitlab/database/load_balancing/configuration_spec.rb

@@ -7,7 +7,10 @@ RSpec.describe Gitlab::Database::LoadBalancing::Configuration do
     config = ActiveRecord::DatabaseConfigurations::HashConfig
       .new('main', 'test', configuration_hash)
 
-    double(:model, connection_db_config: config)
+    double(:model,
+      connection_db_config: config,
+      connection_specification_name: ActiveRecord::Base.connection_specification_name
+    )
   end
 
   describe '.for_model' do

spec/lib/gitlab/database/load_balancing/setup_spec.rb

@@ -23,7 +23,10 @@ RSpec.describe Gitlab::Database::LoadBalancing::Setup do
         env_name: 'test',
         name: 'main'
       )
-      model = double(:model, connection_db_config: config)
+      model = double(:model,
+        connection_db_config: config,
+        connection_specification_name: ActiveRecord::Base.connection_specification_name
+      )
 
       expect(ActiveRecord::DatabaseConfigurations::HashConfig)
         .to receive(:new)

spec/lib/gitlab/database/load_balancing/sticking_spec.rb

@@ -4,7 +4,7 @@ require 'spec_helper'
 
 RSpec.describe Gitlab::Database::LoadBalancing::Sticking, :redis do
   let(:sticking) do
-    described_class.new(ActiveRecord::Base.connection.load_balancer)
+    described_class.new(ActiveRecord::Base.connection.load_balancer, ActiveRecord::Base)
   end
 
   after do