Revert create job service because of load balancing

Currently we still need to run EnsureStageService within a transaction,
because when it runs within in a transaction we are going to stick to
the primary database when using database load balancing. Extracting this
out of the transaction makes it possible to hit into problems with
replication lag in pipeline commit status API, which can cause a lot of
trouble.

app/models/commit_status.rb

@@ -50,9 +50,7 @@ class CommitStatus < ActiveRecord::Base
   ##
   # We still create some CommitStatuses outside of CreatePipelineService.
   #
-  # These are pages deployments and external statuses. We now handle these
-  # jobs using CreateJobService, but we still need to ensure that a job has
-  # a stage assigned. TODO, In future releases we will add model validation.
+  # These are pages deployments and external statuses.
   #
   before_create unless: :importing? do
     Ci::EnsureStageService.new(project, user).execute(self) do |stage|

app/services/ci/create_job_service.rb

-module Ci
-  class CreateJobService < BaseService
-    def execute(subject = nil)
-      (subject || yield).tap do |subject|
-        Ci::EnsureStageService.new(project, current_user)
-          .execute(subject)
-
-        subject.save
-      end
-    end
-  end
-end

app/services/projects/update_pages_service.rb

@@ -58,7 +58,6 @@ module Projects
     end
 
     def create_status
-      Ci::CreateJobService.new(project, build.user).execute do
       GenericCommitStatus.new(
         project: project,
         pipeline: build.pipeline,
@@ -68,7 +67,6 @@ module Projects
         name: 'pages:deploy'
       )
     end
-    end
 
     def extract_archive!(temp_path)
       if artifacts.ends_with?('.tar.gz') || artifacts.ends_with?('.tgz')

db/post_migrate/20180119121225_remove_redundant_pipeline_stages.rb

@@ -4,6 +4,21 @@ class RemoveRedundantPipelineStages < ActiveRecord::Migration
   DOWNTIME = false
 
   def up
+    remove_concurrent_index :ci_stages, [:pipeline_id, :name]
+
+    remove_redundant_pipeline_stages!
+
+    add_concurrent_index :ci_stages, [:pipeline_id, :name], unique: true
+  end
+
+  def down
+    remove_concurrent_index :ci_stages, [:pipeline_id, :name], unique: true
+    add_concurrent_index :ci_stages, [:pipeline_id, :name]
+  end
+
+  private
+
+  def remove_redundant_pipeline_stages!
     redundant_stages_ids = <<~SQL
       SELECT id FROM ci_stages WHERE (pipeline_id, name) IN (
         SELECT pipeline_id, name FROM ci_stages
@@ -27,8 +42,4 @@ class RemoveRedundantPipelineStages < ActiveRecord::Migration
       SQL
     end
   end
-
-  def down
-    # noop
-  end
 end

db/post_migrate/20180125111139_add_unique_pipeline_stage_name_index.rb

-class AddUniquePipelineStageNameIndex < ActiveRecord::Migration
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-
-  disable_ddl_transaction!
-
-  def up
-    remove_concurrent_index :ci_stages, [:pipeline_id, :name]
-    add_concurrent_index :ci_stages, [:pipeline_id, :name], unique: true
-  end
-
-  def down
-    remove_concurrent_index :ci_stages, [:pipeline_id, :name], unique: true
-    add_concurrent_index :ci_stages, [:pipeline_id, :name]
-  end
-end

lib/api/commit_statuses.rb

@@ -69,7 +69,6 @@ module API
         name = params[:name] || params[:context] || 'default'
 
         pipeline = @project.pipeline_for(ref, commit.sha)
-
         unless pipeline
           pipeline = @project.pipelines.create!(
             source: :external,
@@ -91,14 +90,7 @@ module API
         optional_attributes =
           attributes_for_keys(%w[target_url description coverage])
 
-        status.assign_attributes(optional_attributes) if optional_attributes.any?
-
-        if status.new_record?
-          Ci::CreateJobService.new(@project, current_user).execute(status)
-        else
-          status.save if status.changed?
-        end
-
+        status.update(optional_attributes) if optional_attributes.any?
         render_validation_error!(status) if status.invalid?
 
         begin

spec/services/ci/create_job_service_spec.rb

-require 'spec_helper'
-
-describe Ci::CreateJobService, '#execute' do
-  set(:project) { create(:project, :repository) }
-  let(:user) { create(:admin) }
-  let(:status) { build(:ci_build) }
-  let(:service) { described_class.new(project, user) }
-
-  it 'persists job object instantiated in the block' do
-    expect(service.execute { status }).to be_persisted
-  end
-
-  it 'persists a job instance passed as an argument' do
-    expect(service.execute(status)).to be_persisted
-  end
-
-  it 'ensures that a job has a stage assigned' do
-    expect(service.execute(status).stage_id).to be_present
-  end
-
-  it 'does not raise error if status is invalid' do
-    status.name = nil
-
-    expect(service.execute(status)).not_to be_persisted
-  end
-end