17 files changed, 443 insertions, 44 deletions

diff --git a/lib/gitlab/data_builder/push.rb b/lib/gitlab/data_builder/push.rb
index 4f81863da35..d76aa38f741 100644
--- a/lib/gitlab/data_builder/push.rb
+++ b/lib/gitlab/data_builder/push.rb
@@ -83,7 +83,7 @@ module Gitlab
           tag = repository.find_tag(tag_name)
 
           if tag
-            commit = repository.commit(tag.target)
+            commit = repository.commit(tag.dereferenced_target)
             commit.try(:sha)
           end
         else
diff --git a/lib/gitlab/ee_compat_check.rb b/lib/gitlab/ee_compat_check.rb
new file mode 100644
index 00000000000..b1a6d5fe0f6
--- /dev/null
+++ b/lib/gitlab/ee_compat_check.rb
@@ -0,0 +1,261 @@
+# rubocop: disable Rails/Output
+module Gitlab
+  # Checks if a set of migrations requires downtime or not.
+  class EeCompatCheck
+    EE_REPO = 'https://gitlab.com/gitlab-org/gitlab-ee.git'.freeze
+
+    attr_reader :ce_branch, :check_dir, :ce_repo
+
+    def initialize(branch:, check_dir:, ce_repo: nil)
+      @ce_branch = branch
+      @check_dir = check_dir
+      @ce_repo = ce_repo || 'https://gitlab.com/gitlab-org/gitlab-ce.git'
+    end
+
+    def check
+      ensure_ee_repo
+      delete_patches
+
+      generate_patch(ce_branch, ce_patch_full_path)
+
+      Dir.chdir(check_dir) do
+        step("In the #{check_dir} directory")
+
+        step("Pulling latest master", %w[git pull --ff-only origin master])
+
+        status = catch(:halt_check) do
+          ce_branch_compat_check!
+
+          delete_ee_branch_locally
+
+          ee_branch_presence_check!
+
+          ee_branch_compat_check!
+        end
+
+        delete_ee_branch_locally
+        delete_patches
+
+        if status.nil?
+          true
+        else
+          false
+        end
+      end
+    end
+
+    private
+
+    def ensure_ee_repo
+      if Dir.exist?(check_dir)
+        step("#{check_dir} already exists")
+      else
+        cmd = %W[git clone --branch master --single-branch --depth 1 #{EE_REPO} #{check_dir}]
+        step("Cloning #{EE_REPO} into #{check_dir}", cmd)
+      end
+    end
+
+    def ce_branch_compat_check!
+      cmd = %W[git apply --check #{ce_patch_full_path}]
+      status = step("Checking if #{ce_patch_name} applies cleanly to EE/master", cmd)
+
+      if status.zero?
+        puts ce_applies_cleanly_msg(ce_branch)
+        throw(:halt_check)
+      end
+    end
+
+    def ee_branch_presence_check!
+      status = step("Fetching origin/#{ee_branch}", %W[git fetch origin #{ee_branch}])
+
+      unless status.zero?
+        puts
+        puts ce_branch_doesnt_apply_cleanly_and_no_ee_branch_msg
+
+        throw(:halt_check, :ko)
+      end
+    end
+
+    def ee_branch_compat_check!
+      step("Checking out origin/#{ee_branch}", %W[git checkout -b #{ee_branch} FETCH_HEAD])
+
+      generate_patch(ee_branch, ee_patch_full_path)
+      cmd = %W[git apply --check #{ee_patch_full_path}]
+      status = step("Checking if #{ee_patch_name} applies cleanly to EE/master", cmd)
+
+      unless status.zero?
+        puts
+        puts ee_branch_doesnt_apply_cleanly_msg
+
+        throw(:halt_check, :ko)
+      end
+
+      puts
+      puts ee_applies_cleanly_msg
+    end
+
+    def generate_patch(branch, filepath)
+      FileUtils.rm(filepath, force: true)
+
+      depth = 0
+      loop do
+        depth += 10
+        step("Fetching origin/master", %W[git fetch origin master --depth=#{depth}])
+        status = step("Finding merge base with master", %W[git merge-base FETCH_HEAD #{branch}])
+
+        break if status.zero? || depth > 500
+      end
+
+      raise "#{branch} is too far behind master, please rebase it!" if depth > 500
+
+      step("Generating the patch against master")
+      output, status = Gitlab::Popen.popen(%w[git format-patch FETCH_HEAD --stdout])
+      throw(:halt_check, :ko) unless status.zero?
+
+      File.write(filepath, output)
+      throw(:halt_check, :ko) unless File.exist?(filepath)
+    end
+
+    def delete_ee_branch_locally
+      command(%w[git checkout master])
+      step("Deleting the local #{ee_branch} branch", %W[git branch -D #{ee_branch}])
+    end
+
+    def delete_patches
+      step("Deleting #{ce_patch_full_path}")
+      FileUtils.rm(ce_patch_full_path, force: true)
+
+      step("Deleting #{ee_patch_full_path}")
+      FileUtils.rm(ee_patch_full_path, force: true)
+    end
+
+    def ce_patch_name
+      @ce_patch_name ||= "#{ce_branch}.patch"
+    end
+
+    def ce_patch_full_path
+      @ce_patch_full_path ||= File.expand_path(ce_patch_name, check_dir)
+    end
+
+    def ee_branch
+      @ee_branch ||= "#{ce_branch}-ee"
+    end
+
+    def ee_patch_name
+      @ee_patch_name ||= "#{ee_branch}.patch"
+    end
+
+    def ee_patch_full_path
+      @ee_patch_full_path ||= File.expand_path(ee_patch_name, check_dir)
+    end
+
+    def step(desc, cmd = nil)
+      puts "\n=> #{desc}\n"
+
+      if cmd
+        puts "\n$ #{cmd.join(' ')}"
+        command(cmd)
+      end
+    end
+
+    def command(cmd)
+      output, status = Gitlab::Popen.popen(cmd)
+      puts output
+
+      status
+    end
+
+    def ce_applies_cleanly_msg(ce_branch)
+      <<-MSG.strip_heredoc
+        =================================================================
+        🎉 Congratulations!! 🎉
+
+        The #{ce_branch} branch applies cleanly to EE/master!
+
+        Much ❤️!!
+        =================================================================\n
+      MSG
+    end
+
+    def ce_branch_doesnt_apply_cleanly_and_no_ee_branch_msg
+      <<-MSG.strip_heredoc
+        =================================================================
+        💥 Oh no! 💥
+
+        The #{ce_branch} branch does not apply cleanly to the current
+        EE/master, and no #{ee_branch} branch was found in the EE repository.
+
+        Please create a #{ee_branch} branch that includes changes from
+        #{ce_branch} but also specific changes than can be applied cleanly
+        to EE/master.
+
+        There are different ways to create such branch:
+
+        1. Create a new branch based on the CE branch and rebase it on top of EE/master
+
+          # In the EE repo
+          $ git fetch #{ce_repo} #{ce_branch}
+          $ git checkout -b #{ee_branch} FETCH_HEAD
+
+          # You can squash the #{ce_branch} commits into a single "Port of #{ce_branch} to EE" commit
+          # before rebasing to limit the conflicts-resolving steps during the rebase
+          $ git fetch origin
+          $ git rebase origin/master
+
+          At this point you will likely have conflicts.
+          Solve them, and continue/finish the rebase.
+
+          You can squash the #{ce_branch} commits into a single "Port of #{ce_branch} to EE".
+
+        2. Create a new branch from master and cherry-pick your CE commits
+
+          # In the EE repo
+          $ git fetch origin
+          $ git checkout -b #{ee_branch} FETCH_HEAD
+          $ git fetch #{ce_repo} #{ce_branch}
+          $ git cherry-pick SHA # Repeat for all the commits you want to pick
+
+          You can squash the #{ce_branch} commits into a single "Port of #{ce_branch} to EE" commit.
+
+        Don't forget to push your branch to #{EE_REPO}:
+
+          # In the EE repo
+          $ git push origin #{ee_branch}
+
+        You can then retry this failed build, and hopefully it should pass.
+
+        Stay 💪 !
+        =================================================================\n
+      MSG
+    end
+
+    def ee_branch_doesnt_apply_cleanly_msg
+      <<-MSG.strip_heredoc
+        =================================================================
+        💥 Oh no! 💥
+
+        The #{ce_branch} does not apply cleanly to the current
+        EE/master, and even though a #{ee_branch} branch exists in the EE
+        repository, it does not apply cleanly either to EE/master!
+
+        Please update the #{ee_branch}, push it again to #{EE_REPO}, and
+        retry this build.
+
+        Stay 💪 !
+        =================================================================\n
+      MSG
+    end
+
+    def ee_applies_cleanly_msg
+      <<-MSG.strip_heredoc
+        =================================================================
+        🎉 Congratulations!! 🎉
+
+        The #{ee_branch} branch applies cleanly to EE/master!
+
+        Much ❤️!!
+        =================================================================\n
+      MSG
+    end
+  end
+end
diff --git a/lib/gitlab/exclusive_lease.rb b/lib/gitlab/exclusive_lease.rb
index ffe49364379..7e8f35e9298 100644
--- a/lib/gitlab/exclusive_lease.rb
+++ b/lib/gitlab/exclusive_lease.rb
@@ -27,7 +27,7 @@ module Gitlab
   # on begin/ensure blocks to cancel a lease, because the 'ensure' does
   # not always run. Think of 'kill -9' from the Unicorn master for
   # instance.
-  # 
+  #
   # If you find that leases are getting in your way, ask yourself: would
   # it be enough to lower the lease timeout? Another thing that might be
   # appropriate is to only use a lease for bulk/automated operations, and
@@ -48,6 +48,13 @@ module Gitlab
       end
     end
 
+    # Returns true if the key for this lease is set.
+    def exists?
+      Gitlab::Redis.with do |redis|
+        redis.exists(redis_key)
+      end
+    end
+
     # No #cancel method. See comments above!
 
     private
diff --git a/lib/gitlab/fogbugz_import/importer.rb b/lib/gitlab/fogbugz_import/importer.rb
index 65ee85ca5a9..222bcdcbf9c 100644
--- a/lib/gitlab/fogbugz_import/importer.rb
+++ b/lib/gitlab/fogbugz_import/importer.rb
@@ -75,7 +75,7 @@ module Gitlab
 
       def create_label(name)
         params = { title: name, color: nice_label_color(name) }
-        ::Labels::FindOrCreateService.new(project.owner, project, params).execute
+        ::Labels::FindOrCreateService.new(nil, project, params).execute(skip_authorization: true)
       end
 
       def user_info(person_id)
@@ -133,7 +133,7 @@ module Gitlab
             updated_at:  DateTime.parse(bug['dtLastUpdated'])
           )
 
-          issue_labels = ::LabelsFinder.new(project.owner, project_id: project.id, title: labels).execute
+          issue_labels = ::LabelsFinder.new(nil, project_id: project.id, title: labels).execute(skip_authorization: true)
           issue.update_attribute(:label_ids, issue_labels.pluck(:id))
 
           import_issue_comments(issue, comments)
diff --git a/lib/gitlab/github_import/base_formatter.rb b/lib/gitlab/github_import/base_formatter.rb
index 8cacf4f4925..6dbae64a9fe 100644
--- a/lib/gitlab/github_import/base_formatter.rb
+++ b/lib/gitlab/github_import/base_formatter.rb
@@ -10,7 +10,9 @@ module Gitlab
       end
 
       def create!
-        self.klass.create!(self.attributes)
+        project.public_send(project_association).find_or_create_by!(find_condition) do |record|
+          record.attributes = attributes
+        end
       end
 
       private
diff --git a/lib/gitlab/github_import/client.rb b/lib/gitlab/github_import/client.rb
index 7f424b74efb..85df6547a67 100644
--- a/lib/gitlab/github_import/client.rb
+++ b/lib/gitlab/github_import/client.rb
@@ -105,18 +105,20 @@ module Gitlab
         data = api.send(method, *args)
         return data unless data.is_a?(Array)
 
+        last_response = api.last_response
+
         if block_given?
           yield data
-          each_response_page(&block)
+          # api.last_response could change while we're yielding (e.g. fetching labels for each PR)
+          # so we cache our own last response
+          each_response_page(last_response, &block)
         else
-          each_response_page { |page| data.concat(page) }
+          each_response_page(last_response) { |page| data.concat(page) }
           data
         end
       end
 
-      def each_response_page
-        last_response = api.last_response
-
+      def each_response_page(last_response)
         while last_response.rels[:next]
           sleep rate_limit_sleep_time if rate_limit_exceed?
           last_response = last_response.rels[:next].get
diff --git a/lib/gitlab/github_import/importer.rb b/lib/gitlab/github_import/importer.rb
index 4b70f33a851..ecc28799737 100644
--- a/lib/gitlab/github_import/importer.rb
+++ b/lib/gitlab/github_import/importer.rb
@@ -24,7 +24,8 @@ module Gitlab
         import_milestones
         import_issues
         import_pull_requests
-        import_comments
+        import_comments(:issues)
+        import_comments(:pull_requests)
         import_wiki
         import_releases
         handle_errors
@@ -48,7 +49,7 @@ module Gitlab
       end
 
       def import_labels
-        client.labels(repo, per_page: 100) do |labels|
+        fetch_resources(:labels, repo, per_page: 100) do |labels|
           labels.each do |raw|
             begin
               label = LabelFormatter.new(project, raw).create!
@@ -61,7 +62,7 @@ module Gitlab
       end
 
       def import_milestones
-        client.milestones(repo, state: :all, per_page: 100) do |milestones|
+        fetch_resources(:milestones, repo, state: :all, per_page: 100) do |milestones|
           milestones.each do |raw|
             begin
               MilestoneFormatter.new(project, raw).create!
@@ -73,7 +74,7 @@ module Gitlab
       end
 
       def import_issues
-        client.issues(repo, state: :all, sort: :created, direction: :asc, per_page: 100) do |issues|
+        fetch_resources(:issues, repo, state: :all, sort: :created, direction: :asc, per_page: 100) do |issues|
           issues.each do |raw|
             gh_issue = IssueFormatter.new(project, raw)
 
@@ -90,7 +91,7 @@ module Gitlab
       end
 
       def import_pull_requests
-        client.pull_requests(repo, state: :all, sort: :created, direction: :asc, per_page: 100) do |pull_requests|
+        fetch_resources(:pull_requests, repo, state: :all, sort: :created, direction: :asc, per_page: 100) do |pull_requests|
           pull_requests.each do |raw|
             pull_request = PullRequestFormatter.new(project, raw)
             next unless pull_request.valid?
@@ -132,8 +133,15 @@ module Gitlab
       end
 
       def apply_labels(issuable, raw_issuable)
-        if raw_issuable.labels.count > 0
-          label_ids = raw_issuable.labels
+        # GH returns labels for issues but not for pull requests!
+        labels = if issuable.is_a?(MergeRequest)
+                   client.labels_for_issue(repo, raw_issuable.number)
+                 else
+                   raw_issuable.labels
+                 end
+
+        if labels.count > 0
+          label_ids = labels
             .map { |attrs| @labels[attrs.name] }
             .compact
 
@@ -141,23 +149,35 @@ module Gitlab
         end
       end
 
-      def import_comments
-        client.issues_comments(repo, per_page: 100) do |comments|
-          create_comments(comments, :issue)
-        end
+      def import_comments(issuable_type)
+        resource_type = "#{issuable_type}_comments".to_sym
+
+        # Two notes here:
+        # 1. We don't have a distinctive attribute for comments (unlike issues iid), so we fetch the last inserted note,
+        # compare it against every comment in the current imported page until we find match, and that's where start importing
+        # 2. GH returns comments for _both_ issues and PRs through issues_comments API, while pull_requests_comments returns
+        # only comments on diffs, so select last note not based on noteable_type but on line_code
+        line_code_is = issuable_type == :pull_requests ? 'NOT NULL' : 'NULL'
+        last_note    = project.notes.where("line_code IS #{line_code_is}").last
+
+        fetch_resources(resource_type, repo, per_page: 100) do |comments|
+          if last_note
+            discard_inserted_comments(comments, last_note)
+            last_note = nil
+          end
 
-        client.pull_requests_comments(repo, per_page: 100) do |comments|
-          create_comments(comments, :pull_request)
+          create_comments(comments)
         end
       end
 
-      def create_comments(comments, issuable_type)
+      def create_comments(comments)
         ActiveRecord::Base.no_touching do
           comments.each do |raw|
             begin
-              comment        = CommentFormatter.new(project, raw)
-              issuable_class = issuable_type == :issue ? Issue : MergeRequest
-              iid            = raw.send("#{issuable_type}_url").split('/').last # GH doesn't return parent ID directly
+              comment         = CommentFormatter.new(project, raw)
+              # GH does not return info about comment's parent, so we guess it by checking its URL!
+              *_, parent, iid = URI(raw.html_url).path.split('/')
+              issuable_class = parent == 'issues' ? Issue : MergeRequest
               issuable       = issuable_class.find_by_iid(iid)
               next unless issuable
 
@@ -169,6 +189,24 @@ module Gitlab
         end
       end
 
+      def discard_inserted_comments(comments, last_note)
+        last_note_attrs = nil
+
+        cut_off_index = comments.find_index do |raw|
+          comment           = CommentFormatter.new(project, raw)
+          comment_attrs     = comment.attributes
+          last_note_attrs ||= last_note.slice(*comment_attrs.keys)
+
+          comment_attrs.with_indifferent_access == last_note_attrs
+        end
+
+        # No matching resource in the collection, which means we got halted right on the end of the last page, so all good
+        return unless cut_off_index
+
+        # Otherwise, remove the resources we've already inserted
+        comments.shift(cut_off_index + 1)
+      end
+
       def import_wiki
         unless project.wiki.repository_exists?
           wiki = WikiFormatter.new(project)
@@ -184,7 +222,7 @@ module Gitlab
       end
 
       def import_releases
-        client.releases(repo, per_page: 100) do |releases|
+        fetch_resources(:releases, repo, per_page: 100) do |releases|
           releases.each do |raw|
             begin
               gh_release = ReleaseFormatter.new(project, raw)
@@ -195,6 +233,47 @@ module Gitlab
           end
         end
       end
+
+      def fetch_resources(resource_type, *opts)
+        return if imported?(resource_type)
+
+        opts.last.merge!(page: current_page(resource_type))
+
+        client.public_send(resource_type, *opts) do |resources|
+          yield resources
+          increment_page(resource_type)
+        end
+
+        imported!(resource_type)
+      end
+
+      def imported?(resource_type)
+        Rails.cache.read("#{cache_key_prefix}:#{resource_type}:imported")
+      end
+
+      def imported!(resource_type)
+        Rails.cache.write("#{cache_key_prefix}:#{resource_type}:imported", true, ex: 1.day)
+      end
+
+      def increment_page(resource_type)
+        key = "#{cache_key_prefix}:#{resource_type}:current-page"
+
+        # Rails.cache.increment calls INCRBY directly on the value stored under the key, which is
+        # a serialized ActiveSupport::Cache::Entry, so it will return an error by Redis, hence this ugly work-around
+        page = Rails.cache.read(key)
+        page += 1
+        Rails.cache.write(key, page)
+
+        page
+      end
+
+      def current_page(resource_type)
+        Rails.cache.fetch("#{cache_key_prefix}:#{resource_type}:current-page", ex: 1.day) { 1 }
+      end
+
+      def cache_key_prefix
+        @cache_key_prefix ||= "github-import:#{project.id}"
+      end
     end
   end
 end
diff --git a/lib/gitlab/github_import/issue_formatter.rb b/lib/gitlab/github_import/issue_formatter.rb
index 77621de9f4c..8c32ac59fc5 100644
--- a/lib/gitlab/github_import/issue_formatter.rb
+++ b/lib/gitlab/github_import/issue_formatter.rb
@@ -20,8 +20,12 @@ module Gitlab
         raw_data.comments > 0
       end
 
-      def klass
-        Issue
+      def project_association
+        :issues
+      end
+
+      def find_condition
+        { iid: number }
       end
 
       def number
diff --git a/lib/gitlab/github_import/label_formatter.rb b/lib/gitlab/github_import/label_formatter.rb
index 942dfb3312b..211ccdc51bb 100644
--- a/lib/gitlab/github_import/label_formatter.rb
+++ b/lib/gitlab/github_import/label_formatter.rb
@@ -9,14 +9,14 @@ module Gitlab
         }
       end
 
-      def klass
-        Label
+      def project_association
+        :labels
       end
 
       def create!
         params  = attributes.except(:project)
-        service = ::Labels::FindOrCreateService.new(project.owner, project, params)
-        label   = service.execute
+        service = ::Labels::FindOrCreateService.new(nil, project, params)
+        label   = service.execute(skip_authorization: true)
 
         raise ActiveRecord::RecordInvalid.new(label) unless label.persisted?
 
diff --git a/lib/gitlab/github_import/milestone_formatter.rb b/lib/gitlab/github_import/milestone_formatter.rb
index b2fa524cf5b..401dd962521 100644
--- a/lib/gitlab/github_import/milestone_formatter.rb
+++ b/lib/gitlab/github_import/milestone_formatter.rb
@@ -14,8 +14,12 @@ module Gitlab
         }
       end
 
-      def klass
-        Milestone
+      def project_association
+        :milestones
+      end
+
+      def find_condition
+        { iid: raw_data.number }
       end
 
       private
diff --git a/lib/gitlab/github_import/pull_request_formatter.rb b/lib/gitlab/github_import/pull_request_formatter.rb
index 1408683100f..b9a227fb11a 100644
--- a/lib/gitlab/github_import/pull_request_formatter.rb
+++ b/lib/gitlab/github_import/pull_request_formatter.rb
@@ -24,8 +24,12 @@ module Gitlab
         }
       end
 
-      def klass
-        MergeRequest
+      def project_association
+        :merge_requests
+      end
+
+      def find_condition
+        { iid: number }
       end
 
       def number
diff --git a/lib/gitlab/github_import/release_formatter.rb b/lib/gitlab/github_import/release_formatter.rb
index 73d643b00ad..1ad702a6058 100644
--- a/lib/gitlab/github_import/release_formatter.rb
+++ b/lib/gitlab/github_import/release_formatter.rb
@@ -11,8 +11,12 @@ module Gitlab
         }
       end
 
-      def klass
-        Release
+      def project_association
+        :releases
+      end
+
+      def find_condition
+        { tag: raw_data.tag_name }
       end
 
       def valid?
diff --git a/lib/gitlab/google_code_import/importer.rb b/lib/gitlab/google_code_import/importer.rb
index 6a68e786b4f..1f4edc36928 100644
--- a/lib/gitlab/google_code_import/importer.rb
+++ b/lib/gitlab/google_code_import/importer.rb
@@ -101,7 +101,7 @@ module Gitlab
             state:       raw_issue['state'] == 'closed' ? 'closed' : 'opened'
           )
 
-          issue_labels = ::LabelsFinder.new(project.owner, project_id: project.id, title: labels).execute
+          issue_labels = ::LabelsFinder.new(nil, project_id: project.id, title: labels).execute(skip_authorization: true)
           issue.update_attribute(:label_ids, issue_labels.pluck(:id))
 
           import_issue_comments(issue, comments)
@@ -235,7 +235,7 @@ module Gitlab
 
       def create_label(name)
         params = { name: name, color: nice_label_color(name) }
-        ::Labels::FindOrCreateService.new(project.owner, project, params).execute
+        ::Labels::FindOrCreateService.new(nil, project, params).execute(skip_authorization: true)
       end
 
       def format_content(raw_content)
diff --git a/lib/gitlab/issues_labels.rb b/lib/gitlab/issues_labels.rb
index 01a2c19ab23..b8ca7f2f55f 100644
--- a/lib/gitlab/issues_labels.rb
+++ b/lib/gitlab/issues_labels.rb
@@ -19,7 +19,7 @@ module Gitlab
         ]
 
         labels.each do |params|
-          ::Labels::FindOrCreateService.new(project.owner, project).execute(params)
+          ::Labels::FindOrCreateService.new(nil, project, params).execute(skip_authorization: true)
         end
       end
     end
diff --git a/lib/gitlab/mail_room.rb b/lib/gitlab/mail_room.rb
index 12999a90a29..a5220d92312 100644
--- a/lib/gitlab/mail_room.rb
+++ b/lib/gitlab/mail_room.rb
@@ -33,7 +33,12 @@ module Gitlab
         config[:mailbox] = 'inbox' if config[:mailbox].nil?
 
         if config[:enabled] && config[:address]
-          config[:redis_url] = Gitlab::Redis.new(rails_env).url
+          gitlab_redis = Gitlab::Redis.new(rails_env)
+          config[:redis_url] = gitlab_redis.url
+
+          if gitlab_redis.sentinels?
+            config[:sentinels] = gitlab_redis.sentinels
+          end
         end
 
         config
diff --git a/lib/gitlab/optimistic_locking.rb b/lib/gitlab/optimistic_locking.rb
new file mode 100644
index 00000000000..879d46446b3
--- /dev/null
+++ b/lib/gitlab/optimistic_locking.rb
@@ -0,0 +1,19 @@
+module Gitlab
+  module OptimisticLocking
+    extend self
+
+    def retry_lock(subject, retries = 100, &block)
+      loop do
+        begin
+          ActiveRecord::Base.transaction do
+            return block.call(subject)
+          end
+        rescue ActiveRecord::StaleObjectError
+          retries -= 1
+          raise unless retries >= 0
+          subject.reload
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/redis.rb b/lib/gitlab/redis.rb
index c649da8c426..9226da2d6b1 100644
--- a/lib/gitlab/redis.rb
+++ b/lib/gitlab/redis.rb
@@ -63,6 +63,14 @@ module Gitlab
       raw_config_hash[:url]
     end
 
+    def sentinels
+      raw_config_hash[:sentinels]
+    end
+
+    def sentinels?
+      sentinels && !sentinels.empty?
+    end
+
     private
 
     def redis_store_options