Make `RackMiddleware` to prefer `sticking` instead of `model.sticking`

Before this change we would store `model` for the purpose of understanding
sticking context for a object. This changes to prefer `sticking` which
is directly connected to `LB` context on which the `sticking` is evaluated.

lib/gitlab/database/load_balancing/rack_middleware.rb

@@ -38,8 +38,8 @@ module Gitlab
         def unstick_or_continue_sticking(env)
           namespaces_and_ids = sticking_namespaces(env)
 
-          namespaces_and_ids.each do |(model, namespace, id)|
-            model.sticking.unstick_or_continue_sticking(namespace, id)
+          namespaces_and_ids.each do |(sticking, namespace, id)|
+            sticking.unstick_or_continue_sticking(namespace, id)
           end
         end
 
@@ -47,8 +47,8 @@ module Gitlab
         def stick_if_necessary(env)
           namespaces_and_ids = sticking_namespaces(env)
 
-          namespaces_and_ids.each do |model, namespace, id|
-            model.sticking.stick_if_necessary(namespace, id)
+          namespaces_and_ids.each do |sticking, namespace, id|
+            sticking.stick_if_necessary(namespace, id)
           end
         end
 
@@ -74,7 +74,7 @@ module Gitlab
             # models that support load balancing. In the future (if we
             # determined this to be OK) we may be able to relax this.
             ::Gitlab::Database::LoadBalancing.base_models.map do |model|
-              [model, :user, warden.user.id]
+              [model.sticking, :user, warden.user.id]
             end
           elsif env[STICK_OBJECT].present?
             env[STICK_OBJECT].to_a

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)
+          @model.sticking = Sticking.new(lb)
         end
 
         def setup_service_discovery

lib/gitlab/database/load_balancing/sticking.rb

@@ -10,9 +10,8 @@ module Gitlab
         # the primary.
         EXPIRATION = 30
 
-        def initialize(load_balancer, model)
+        def initialize(load_balancer)
           @load_balancer = load_balancer
-          @model = model
         end
 
         # Unsticks or continues sticking the current request.
@@ -28,7 +27,7 @@ module Gitlab
           unstick_or_continue_sticking(namespace, id)
 
           env[RackMiddleware::STICK_OBJECT] ||= Set.new
-          env[RackMiddleware::STICK_OBJECT] << [@model, namespace, id]
+          env[RackMiddleware::STICK_OBJECT] << [self, namespace, id]
         end
 
         # Sticks to the primary if a write was performed.

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

@@ -6,12 +6,12 @@ RSpec.describe Gitlab::Database::LoadBalancing::RackMiddleware, :redis do
   let(:app) { double(:app) }
   let(:middleware) { described_class.new(app) }
   let(:warden_user) { double(:warden, user: double(:user, id: 42)) }
-  let(:single_sticking_object) { Set.new([[ActiveRecord::Base, :user, 42]]) }
+  let(:single_sticking_object) { Set.new([[ActiveRecord::Base.sticking, :user, 42]]) }
   let(:multiple_sticking_objects) do
     Set.new([
-      [ActiveRecord::Base, :user, 42],
-      [ActiveRecord::Base, :runner, '123456789'],
-      [ActiveRecord::Base, :runner, '1234']
+      [ActiveRecord::Base.sticking, :user, 42],
+      [ActiveRecord::Base.sticking, :runner, '123456789'],
+      [ActiveRecord::Base.sticking, :runner, '1234']
     ])
   end
 

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, ActiveRecord::Base)
+    described_class.new(ActiveRecord::Base.connection.load_balancer)
   end
 
   after do