diff --git a/CHANGELOG b/CHANGELOG
index e2d65c632dc..1cf8730cda1 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -71,6 +71,7 @@ v 8.9.0 (unreleased)
   - Todos will display target state if issuable target is 'Closed' or 'Merged'
   - Validate only and except regexp
   - Fix bug when sorting issues by milestone due date and filtering by two or more labels
+  - POST to API /projects/:id/runners/:runner_id would give 409 if the runner was already enabled for this project
   - Add support for using Yubikeys (U2F) for two-factor authentication
   - Link to blank group icon doesn't throw a 404 anymore
   - Remove 'main language' feature
@@ -86,6 +87,7 @@ v 8.9.0 (unreleased)
   - Make Omniauth providers specs to not modify global configuration
   - Remove unused JiraIssue class and replace references with ExternalIssue. !4659 (Ilan Shamir)
   - Make authentication service for Container Registry to be compatible with < Docker 1.11
+  - Make it possible to lock a runner from being enabled for other projects
   - Add Application Setting to configure Container Registry token expire delay (default 5min)
   - Cache assigned issue and merge request counts in sidebar nav
   - Use Knapsack only in CI environment
diff --git a/app/controllers/admin/runner_projects_controller.rb b/app/controllers/admin/runner_projects_controller.rb
index d25619d94e0..bf20c5305a7 100644
--- a/app/controllers/admin/runner_projects_controller.rb
+++ b/app/controllers/admin/runner_projects_controller.rb
@@ -1,15 +1,14 @@
 class Admin::RunnerProjectsController < Admin::ApplicationController
   before_action :project, only: [:create]
 
-  def index
-    @runner_projects = project.runner_projects.all
-    @runner_project = project.runner_projects.new
-  end
-
   def create
     @runner = Ci::Runner.find(params[:runner_project][:runner_id])
 
-    if @runner.assign_to(@project, current_user)
+    return head(403) if @runner.is_shared? || @runner.locked?
+
+    runner_project = @runner.assign_to(@project, current_user)
+
+    if runner_project.persisted?
       redirect_to admin_runner_path(@runner)
     else
       redirect_to admin_runner_path(@runner), alert: 'Failed adding runner to project'
diff --git a/app/controllers/projects/runner_projects_controller.rb b/app/controllers/projects/runner_projects_controller.rb
index bedeb4a295c..dc1a18f8d42 100644
--- a/app/controllers/projects/runner_projects_controller.rb
+++ b/app/controllers/projects/runner_projects_controller.rb
@@ -6,11 +6,13 @@ class Projects::RunnerProjectsController < Projects::ApplicationController
   def create
     @runner = Ci::Runner.find(params[:runner_project][:runner_id])
 
+    return head(403) if @runner.is_shared? || @runner.locked?
     return head(403) unless current_user.ci_authorized_runners.include?(@runner)
 
     path = runners_path(project)
+    runner_project = @runner.assign_to(project, current_user)
 
-    if @runner.assign_to(project, current_user)
+    if runner_project.persisted?
       redirect_to path
     else
       redirect_to path, alert: 'Failed adding runner to project'
diff --git a/app/controllers/projects/runners_controller.rb b/app/controllers/projects/runners_controller.rb
index 0b4fa572501..53c36635efe 100644
--- a/app/controllers/projects/runners_controller.rb
+++ b/app/controllers/projects/runners_controller.rb
@@ -5,10 +5,9 @@ class Projects::RunnersController < Projects::ApplicationController
   layout 'project_settings'
 
   def index
-    @runners = project.runners.ordered
-    @specific_runners = current_user.ci_authorized_runners.
-      where.not(id: project.runners).
-      ordered.page(params[:page]).per(20)
+    @project_runners = project.runners.ordered
+    @assignable_runners = current_user.ci_authorized_runners.
+      assignable_for(project).ordered.page(params[:page]).per(20)
     @shared_runners = Ci::Runner.shared.active
     @shared_runners_count = @shared_runners.count(:all)
   end
diff --git a/app/models/ci/build.rb b/app/models/ci/build.rb
index d618c84e983..2b0bec33131 100644
--- a/app/models/ci/build.rb
+++ b/app/models/ci/build.rb
@@ -300,18 +300,12 @@ module Ci
       project.valid_runners_token? token
     end
 
-    def can_be_served?(runner)
-      return false unless has_tags? || runner.run_untagged?
-
-      (tag_list - runner.tag_list).empty?
-    end
-
     def has_tags?
       tag_list.any?
     end
 
     def any_runners_online?
-      project.any_runners? { |runner| runner.active? && runner.online? && can_be_served?(runner) }
+      project.any_runners? { |runner| runner.active? && runner.online? && runner.can_pick?(self) }
     end
 
     def stuck?
diff --git a/app/models/ci/runner.rb b/app/models/ci/runner.rb
index adb65292208..b64ec79ec2b 100644
--- a/app/models/ci/runner.rb
+++ b/app/models/ci/runner.rb
@@ -4,7 +4,7 @@ module Ci
 
     LAST_CONTACT_TIME = 5.minutes.ago
     AVAILABLE_SCOPES = %w[specific shared active paused online]
-    FORM_EDITABLE = %i[description tag_list active run_untagged]
+    FORM_EDITABLE = %i[description tag_list active run_untagged locked]
 
     has_many :builds, class_name: 'Ci::Build'
     has_many :runner_projects, dependent: :destroy, class_name: 'Ci::RunnerProject'
@@ -26,6 +26,13 @@ module Ci
         .where("ci_runner_projects.gl_project_id = :project_id OR ci_runners.is_shared = true", project_id: project_id)
     end
 
+    scope :assignable_for, ->(project) do
+      # FIXME: That `to_sql` is needed to workaround a weird Rails bug.
+      #        Without that, placeholders would miss one and couldn't match.
+      where(locked: false).
+        where.not("id IN (#{project.runners.select(:id).to_sql})").specific
+    end
+
     validate :tag_constraints
 
     acts_as_taggable
@@ -56,7 +63,7 @@ module Ci
     def assign_to(project, current_user = nil)
       self.is_shared = false if shared?
       self.save
-      project.runner_projects.create!(runner_id: self.id)
+      project.runner_projects.create(runner_id: self.id)
     end
 
     def display_name
@@ -91,6 +98,10 @@ module Ci
       !shared?
     end
 
+    def can_pick?(build)
+      assignable_for?(build.project) && accepting_tags?(build)
+    end
+
     def only_for?(project)
       projects == [project]
     end
@@ -111,5 +122,13 @@ module Ci
           'can not be empty when runner is not allowed to pick untagged jobs')
       end
     end
+
+    def assignable_for?(project)
+      !locked? || projects.exists?(id: project.id)
+    end
+
+    def accepting_tags?(build)
+      (run_untagged? || build.has_tags?) && (build.tag_list - tag_list).empty?
+    end
   end
 end
diff --git a/app/services/ci/register_build_service.rb b/app/services/ci/register_build_service.rb
index f0ed09a629a..9a187f5d694 100644
--- a/app/services/ci/register_build_service.rb
+++ b/app/services/ci/register_build_service.rb
@@ -21,7 +21,7 @@ module Ci
         end
 
       build = builds.find do |build|
-        build.can_be_served?(current_runner)
+        current_runner.can_pick?(build)
       end
 
       if build
diff --git a/app/views/admin/runners/show.html.haml b/app/views/admin/runners/show.html.haml
index e049b40bfab..61abfc6ecbe 100644
--- a/app/views/admin/runners/show.html.haml
+++ b/app/views/admin/runners/show.html.haml
@@ -28,7 +28,7 @@
   .col-md-6
     %h4 Restrict projects for this runner
     - if @runner.projects.any?
-      %table.table
+      %table.table.assigned-projects
         %thead
           %tr
             %th Assigned projects
@@ -44,7 +44,7 @@
                 .pull-right
                   = link_to 'Disable', [:admin, project.namespace.becomes(Namespace), project, runner_project], method: :delete, class: 'btn btn-danger btn-xs'
 
-    %table.table
+    %table.table.unassigned-projects
       %thead
         %tr
           %th Project
diff --git a/app/views/projects/runners/_form.html.haml b/app/views/projects/runners/_form.html.haml
index d62f5c8f131..c45a9d4f81f 100644
--- a/app/views/projects/runners/_form.html.haml
+++ b/app/views/projects/runners/_form.html.haml
@@ -12,6 +12,12 @@
       .checkbox
         = f.check_box :run_untagged
         %span.light Indicates whether this runner can pick jobs without tags
+  .form-group
+    = label :locked, 'Lock to current projects', class: 'control-label'
+    .col-sm-10
+      .checkbox
+        = f.check_box :locked
+        %span.light When a runner is locked, it cannot be assigned to other projects
   .form-group
     = label_tag :token, class: 'control-label' do
       Token
diff --git a/app/views/projects/runners/_runner.html.haml b/app/views/projects/runners/_runner.html.haml
index 96e2aac451f..85225857758 100644
--- a/app/views/projects/runners/_runner.html.haml
+++ b/app/views/projects/runners/_runner.html.haml
@@ -2,8 +2,10 @@
   %h4
     = runner_status_icon(runner)
     %span.monospace
-      - if @runners.include?(runner)
+      - if @project_runners.include?(runner)
         = link_to runner.short_sha, runner_path(runner)
+        - if runner.locked?
+          = icon('lock', class: 'has-tooltip', title: 'Locked to current projects')
         %small
           = link_to edit_namespace_project_runner_path(@project.namespace, @project, runner) do
             %i.fa.fa-edit.btn
@@ -11,7 +13,7 @@
         = runner.short_sha
 
     .pull-right
-      - if @runners.include?(runner)
+      - if @project_runners.include?(runner)
         - if runner.belongs_to_one_project?
           = link_to 'Remove runner', runner_path(runner), data: { confirm: "Are you sure?" }, method: :delete, class: 'btn btn-danger btn-sm'
         - else
diff --git a/app/views/projects/runners/_specific_runners.html.haml b/app/views/projects/runners/_specific_runners.html.haml
index 8ae9f0d95f7..d469dda5b81 100644
--- a/app/views/projects/runners/_specific_runners.html.haml
+++ b/app/views/projects/runners/_specific_runners.html.haml
@@ -17,13 +17,13 @@
       Start runner!
 
 
-- if @runners.any?
+- if @project_runners.any?
   %h4.underlined-title Runners activated for this project
   %ul.bordered-list.activated-specific-runners
-    = render partial: 'runner', collection: @runners, as: :runner
+    = render partial: 'runner', collection: @project_runners, as: :runner
 
-- if @specific_runners.any?
+- if @assignable_runners.any?
   %h4.underlined-title Available specific runners
   %ul.bordered-list.available-specific-runners
-    = render partial: 'runner', collection: @specific_runners, as: :runner
-  = paginate @specific_runners
+    = render partial: 'runner', collection: @assignable_runners, as: :runner
+  = paginate @assignable_runners
diff --git a/app/views/projects/runners/show.html.haml b/app/views/projects/runners/show.html.haml
index f24e1b9144e..61b99f35d74 100644
--- a/app/views/projects/runners/show.html.haml
+++ b/app/views/projects/runners/show.html.haml
@@ -22,6 +22,9 @@
     %tr
       %td Can run untagged jobs
       %td= @runner.run_untagged? ? 'Yes' : 'No'
+    %tr
+      %td Locked to this project
+      %td= @runner.locked? ? 'Yes' : 'No'
     %tr
       %td Tags
       %td
diff --git a/config/routes.rb b/config/routes.rb
index a22559ebabc..e45293cdf7f 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -295,7 +295,7 @@ Rails.application.routes.draw do
           post :repository_check
         end
 
-        resources :runner_projects
+        resources :runner_projects, only: [:create, :destroy]
       end
     end
 
diff --git a/db/migrate/20160509091049_add_locked_to_ci_runner.rb b/db/migrate/20160509091049_add_locked_to_ci_runner.rb
new file mode 100644
index 00000000000..3fbaef3b7f0
--- /dev/null
+++ b/db/migrate/20160509091049_add_locked_to_ci_runner.rb
@@ -0,0 +1,13 @@
+class AddLockedToCiRunner < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default(:ci_runners, :locked, :boolean,
+                            default: false, allow_null: false)
+  end
+
+  def down
+    remove_column(:ci_runners, :locked)
+  end
+end
diff --git a/db/migrate/20160620115026_add_index_on_runners_locked.rb b/db/migrate/20160620115026_add_index_on_runners_locked.rb
new file mode 100644
index 00000000000..dfa5110dea4
--- /dev/null
+++ b/db/migrate/20160620115026_add_index_on_runners_locked.rb
@@ -0,0 +1,12 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddIndexOnRunnersLocked < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def change
+    add_concurrent_index :ci_runners, :locked
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 29f90c47848..7a8377f687c 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160617301627) do
+ActiveRecord::Schema.define(version: 20160620115026) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -287,9 +287,11 @@ ActiveRecord::Schema.define(version: 20160617301627) do
     t.string   "platform"
     t.string   "architecture"
     t.boolean  "run_untagged", default: true,  null: false
+    t.boolean  "locked",       default: false, null: false
   end
 
   add_index "ci_runners", ["description"], name: "index_ci_runners_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
+  add_index "ci_runners", ["locked"], name: "index_ci_runners_on_locked", using: :btree
   add_index "ci_runners", ["token"], name: "index_ci_runners_on_token", using: :btree
   add_index "ci_runners", ["token"], name: "index_ci_runners_on_token_trigram", using: :gin, opclasses: {"token"=>"gin_trgm_ops"}
 
diff --git a/doc/ci/runners/README.md b/doc/ci/runners/README.md
index 400784da617..ddebd987650 100644
--- a/doc/ci/runners/README.md
+++ b/doc/ci/runners/README.md
@@ -96,6 +96,12 @@ To register the runner, run the command below and follow instructions:
 sudo gitlab-ci-multi-runner register
 ```
 
+###  Lock a specific runner from being enabled for other projects
+
+You can configure a runner to assign it exclusively to a project. When a
+runner is locked this way, it can no longer be enabled for other projects.
+This setting is available on each runner in *Project Settings* > *Runners*.
+
 ###  Making an existing Shared Runner Specific
 
 If you are an admin on your GitLab instance,
@@ -128,7 +134,7 @@ the appropriate dependencies to run Rails test suites.
 ### Prevent runner with tags from picking jobs without tags
 
 You can configure a runner to prevent it from picking jobs with tags when
-the runnner does not have tags assigned. This setting is available on each
+the runner does not have tags assigned. This setting is available on each
 runner in *Project Settings* > *Runners*.
 
 ### Be careful with sensitive information
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index 2e397643ed1..3fde7aa989f 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -423,6 +423,7 @@ module API
     class RunnerDetails < Runner
       expose :tag_list
       expose :run_untagged
+      expose :locked
       expose :version, :revision, :platform, :architecture
       expose :contacted_at
       expose :token, if: lambda { |runner, options| options[:current_user].is_admin? || !runner.is_shared? }
diff --git a/lib/api/runners.rb b/lib/api/runners.rb
index 4faba9dc87b..ecc8f2fc5a2 100644
--- a/lib/api/runners.rb
+++ b/lib/api/runners.rb
@@ -49,7 +49,7 @@ module API
         runner = get_runner(params[:id])
         authenticate_update_runner!(runner)
 
-        attrs = attributes_for_keys [:description, :active, :tag_list, :run_untagged]
+        attrs = attributes_for_keys [:description, :active, :tag_list, :run_untagged, :locked]
         if runner.update(attrs)
           present runner, with: Entities::RunnerDetails, current_user: current_user
         else
@@ -96,9 +96,14 @@ module API
 
         runner = get_runner(params[:runner_id])
         authenticate_enable_runner!(runner)
-        Ci::RunnerProject.create(runner: runner, project: user_project)
 
-        present runner, with: Entities::Runner
+        runner_project = runner.assign_to(user_project)
+
+        if runner_project.persisted?
+          present runner, with: Entities::Runner
+        else
+          conflict!("Runner was already enabled for this project")
+        end
       end
 
       # Disable project's runner
@@ -163,6 +168,7 @@ module API
 
       def authenticate_enable_runner!(runner)
         forbidden!("Runner is shared") if runner.is_shared?
+        forbidden!("Runner is locked") if runner.locked?
         return if current_user.is_admin?
         forbidden!("No access granted") unless user_can_access_runner?(runner)
       end
diff --git a/lib/ci/api/runners.rb b/lib/ci/api/runners.rb
index 0c41f22c7c5..bcc82969eb3 100644
--- a/lib/ci/api/runners.rb
+++ b/lib/ci/api/runners.rb
@@ -28,12 +28,9 @@ module Ci
         post "register" do
           required_attributes! [:token]
 
-          attributes = { description: params[:description],
-                         tag_list: params[:tag_list] }
-
-          unless params[:run_untagged].nil?
-            attributes[:run_untagged] = params[:run_untagged]
-          end
+          attributes = attributes_for_keys(
+            [:description, :tag_list, :run_untagged, :locked]
+          )
 
           runner =
             if runner_registration_token_valid?
diff --git a/spec/factories/ci/commits.rb b/spec/factories/ci/pipelines.rb
similarity index 100%
rename from spec/factories/ci/commits.rb
rename to spec/factories/ci/pipelines.rb
diff --git a/spec/features/admin/admin_runners_spec.rb b/spec/features/admin/admin_runners_spec.rb
index 9499cd4e025..2d297776cb0 100644
--- a/spec/features/admin/admin_runners_spec.rb
+++ b/spec/features/admin/admin_runners_spec.rb
@@ -60,6 +60,40 @@ describe "Admin Runners" do
       it { expect(page).to have_content(@project1.name_with_namespace) }
       it { expect(page).not_to have_content(@project2.name_with_namespace) }
     end
+
+    describe 'enable/create' do
+      before do
+        @project1.runners << runner
+        visit admin_runner_path(runner)
+      end
+
+      it 'enables specific runner for project' do
+        within '.unassigned-projects' do
+          click_on 'Enable'
+        end
+
+        assigned_project = page.find('.assigned-projects')
+
+        expect(assigned_project).to have_content(@project2.path)
+      end
+    end
+
+    describe 'disable/destroy' do
+      before do
+        @project1.runners << runner
+        visit admin_runner_path(runner)
+      end
+
+      it 'enables specific runner for project' do
+        within '.assigned-projects' do
+          click_on 'Disable'
+        end
+
+        new_runner_project = page.find('.unassigned-projects')
+
+        expect(new_runner_project).to have_content(@project1.path)
+      end
+    end
   end
 
   describe 'runners registration token' do
diff --git a/spec/models/build_spec.rb b/spec/models/build_spec.rb
index 5d1fa8226e5..479b7309579 100644
--- a/spec/models/build_spec.rb
+++ b/spec/models/build_spec.rb
@@ -36,32 +36,44 @@ describe Ci::Build, models: true do
     subject { build.ignored? }
 
     context 'if build is not allowed to fail' do
-      before { build.allow_failure = false }
+      before do
+        build.allow_failure = false
+      end
 
       context 'and build.status is success' do
-        before { build.status = 'success' }
+        before do
+          build.status = 'success'
+        end
 
         it { is_expected.to be_falsey }
       end
 
       context 'and build.status is failed' do
-        before { build.status = 'failed' }
+        before do
+          build.status = 'failed'
+        end
 
         it { is_expected.to be_falsey }
       end
     end
 
     context 'if build is allowed to fail' do
-      before { build.allow_failure = true }
+      before do
+        build.allow_failure = true
+      end
 
       context 'and build.status is success' do
-        before { build.status = 'success' }
+        before do
+          build.status = 'success'
+        end
 
         it { is_expected.to be_falsey }
       end
 
       context 'and build.status is failed' do
-        before { build.status = 'failed' }
+        before do
+          build.status = 'failed'
+        end
 
         it { is_expected.to be_truthy }
       end
@@ -75,7 +87,9 @@ describe Ci::Build, models: true do
 
     context 'if build.trace contains text' do
       let(:text) { 'example output' }
-      before { build.trace = text }
+      before do
+        build.trace = text
+      end
 
       it { is_expected.to include(text) }
       it { expect(subject.length).to be >= text.length }
@@ -188,7 +202,9 @@ describe Ci::Build, models: true do
         ]
       end
 
-      before { build.update_attributes(stage: 'stage') }
+      before do
+        build.update_attributes(stage: 'stage')
+      end
 
       it { is_expected.to eq(predefined_variables + yaml_variables) }
 
@@ -199,7 +215,9 @@ describe Ci::Build, models: true do
           ]
         end
 
-        before { build.update_attributes(tag: true) }
+        before do
+          build.update_attributes(tag: true)
+        end
 
         it { is_expected.to eq(tag_variable + predefined_variables + yaml_variables) }
       end
@@ -257,57 +275,6 @@ describe Ci::Build, models: true do
     end
   end
 
-  describe '#can_be_served?' do
-    let(:runner) { create(:ci_runner) }
-
-    before { build.project.runners << runner }
-
-    context 'when runner does not have tags' do
-      it 'can handle builds without tags' do
-        expect(build.can_be_served?(runner)).to be_truthy
-      end
-
-      it 'cannot handle build with tags' do
-        build.tag_list = ['aa']
-        expect(build.can_be_served?(runner)).to be_falsey
-      end
-    end
-
-    context 'when runner has tags' do
-      before { runner.tag_list = ['bb', 'cc'] }
-
-      shared_examples 'tagged build picker' do
-        it 'can handle build with matching tags' do
-          build.tag_list = ['bb']
-          expect(build.can_be_served?(runner)).to be_truthy
-        end
-
-        it 'cannot handle build without matching tags' do
-          build.tag_list = ['aa']
-          expect(build.can_be_served?(runner)).to be_falsey
-        end
-      end
-
-      context 'when runner can pick untagged jobs' do
-        it 'can handle builds without tags' do
-          expect(build.can_be_served?(runner)).to be_truthy
-        end
-
-        it_behaves_like 'tagged build picker'
-      end
-
-      context 'when runner can not pick untagged jobs' do
-        before { runner.run_untagged = false }
-
-        it 'can not handle builds without tags' do
-          expect(build.can_be_served?(runner)).to be_falsey
-        end
-
-        it_behaves_like 'tagged build picker'
-      end
-    end
-  end
-
   describe '#has_tags?' do
     context 'when build has tags' do
       subject { create(:ci_build, tag_list: ['tag']) }
@@ -348,7 +315,7 @@ describe Ci::Build, models: true do
       end
 
       it 'that cannot handle build' do
-        expect_any_instance_of(Ci::Build).to receive(:can_be_served?).and_return(false)
+        expect_any_instance_of(Ci::Runner).to receive(:can_pick?).and_return(false)
         is_expected.to be_falsey
       end
 
@@ -360,7 +327,9 @@ describe Ci::Build, models: true do
 
     %w(pending).each do |state|
       context "if commit_status.status is #{state}" do
-        before { build.status = state }
+        before do
+          build.status = state
+        end
 
         it { is_expected.to be_truthy }
 
@@ -379,7 +348,9 @@ describe Ci::Build, models: true do
 
     %w(success failed canceled running).each do |state|
       context "if commit_status.status is #{state}" do
-        before { build.status = state }
+        before do
+          build.status = state
+        end
 
         it { is_expected.to be_falsey }
       end
@@ -390,7 +361,10 @@ describe Ci::Build, models: true do
     subject { build.artifacts? }
 
     context 'artifacts archive does not exist' do
-      before { build.update_attributes(artifacts_file: nil) }
+      before do
+        build.update_attributes(artifacts_file: nil)
+      end
+
       it { is_expected.to be_falsy }
     end
 
@@ -623,7 +597,9 @@ describe Ci::Build, models: true do
       let!(:build) { create(:ci_build, :trace, :success, :artifacts) }
 
       describe '#erase' do
-        before { build.erase(erased_by: user) }
+        before do
+          build.erase(erased_by: user)
+        end
 
         context 'erased by user' do
           let!(:user) { create(:user, username: 'eraser') }
@@ -660,7 +636,9 @@ describe Ci::Build, models: true do
         end
 
         context 'build has been erased' do
-          before { build.erase }
+          before do
+            build.erase
+          end
 
           it { is_expected.to be true }
         end
@@ -668,7 +646,9 @@ describe Ci::Build, models: true do
 
       context 'metadata and build trace are not available' do
         let!(:build) { create(:ci_build, :success, :artifacts) }
-        before { build.remove_artifacts_metadata! }
+        before do
+          build.remove_artifacts_metadata!
+        end
 
         describe '#erase' do
           it 'should not raise error' do
diff --git a/spec/models/ci/runner_spec.rb b/spec/models/ci/runner_spec.rb
index 5d04d8ffcff..ef65eb99328 100644
--- a/spec/models/ci/runner_spec.rb
+++ b/spec/models/ci/runner_spec.rb
@@ -20,34 +20,36 @@ describe Ci::Runner, models: true do
   end
 
   describe '#display_name' do
-    it 'should return the description if it has a value' do
+    it 'returns the description if it has a value' do
       runner = FactoryGirl.build(:ci_runner, description: 'Linux/Ruby-1.9.3-p448')
       expect(runner.display_name).to eq 'Linux/Ruby-1.9.3-p448'
     end
 
-    it 'should return the token if it does not have a description' do
+    it 'returns the token if it does not have a description' do
       runner = FactoryGirl.create(:ci_runner)
       expect(runner.display_name).to eq runner.description
     end
 
-    it 'should return the token if the description is an empty string' do
+    it 'returns the token if the description is an empty string' do
       runner = FactoryGirl.build(:ci_runner, description: '', token: 'token')
       expect(runner.display_name).to eq runner.token
     end
   end
 
-  describe :assign_to do
+  describe '#assign_to' do
     let!(:project) { FactoryGirl.create :empty_project }
     let!(:shared_runner) { FactoryGirl.create(:ci_runner, :shared) }
 
-    before { shared_runner.assign_to(project) }
+    before do
+      shared_runner.assign_to(project)
+    end
 
     it { expect(shared_runner).to be_specific }
     it { expect(shared_runner.projects).to eq([project]) }
     it { expect(shared_runner.only_for?(project)).to be_truthy }
   end
 
-  describe :online do
+  describe '.online' do
     subject { Ci::Runner.online }
 
     before do
@@ -58,60 +60,269 @@ describe Ci::Runner, models: true do
     it { is_expected.to eq([@runner2])}
   end
 
-  describe :online? do
+  describe '#online?' do
     let(:runner) { FactoryGirl.create(:ci_runner, :shared) }
 
     subject { runner.online? }
 
     context 'never contacted' do
-      before { runner.contacted_at = nil }
+      before do
+        runner.contacted_at = nil
+      end
 
       it { is_expected.to be_falsey }
     end
 
     context 'contacted long time ago time' do
-      before { runner.contacted_at = 1.year.ago }
+      before do
+        runner.contacted_at = 1.year.ago
+      end
 
       it { is_expected.to be_falsey }
     end
 
     context 'contacted 1s ago' do
-      before { runner.contacted_at = 1.second.ago }
+      before do
+        runner.contacted_at = 1.second.ago
+      end
 
       it { is_expected.to be_truthy }
     end
   end
 
-  describe :status do
+  describe '#can_pick?' do
+    let(:project) { create(:project) }
+    let(:pipeline) { create(:ci_pipeline, project: project) }
+    let(:build) { create(:ci_build, pipeline: pipeline) }
+    let(:runner) { create(:ci_runner) }
+
+    before do
+      build.project.runners << runner
+    end
+
+    context 'when runner does not have tags' do
+      it 'can handle builds without tags' do
+        expect(runner.can_pick?(build)).to be_truthy
+      end
+
+      it 'cannot handle build with tags' do
+        build.tag_list = ['aa']
+
+        expect(runner.can_pick?(build)).to be_falsey
+      end
+    end
+
+    context 'when runner has tags' do
+      before do
+        runner.tag_list = ['bb', 'cc']
+      end
+
+      shared_examples 'tagged build picker' do
+        it 'can handle build with matching tags' do
+          build.tag_list = ['bb']
+
+          expect(runner.can_pick?(build)).to be_truthy
+        end
+
+        it 'cannot handle build without matching tags' do
+          build.tag_list = ['aa']
+
+          expect(runner.can_pick?(build)).to be_falsey
+        end
+      end
+
+      context 'when runner can pick untagged jobs' do
+        it 'can handle builds without tags' do
+          expect(runner.can_pick?(build)).to be_truthy
+        end
+
+        it_behaves_like 'tagged build picker'
+      end
+
+      context 'when runner cannot pick untagged jobs' do
+        before do
+          runner.run_untagged = false
+        end
+
+        it 'cannot handle builds without tags' do
+          expect(runner.can_pick?(build)).to be_falsey
+        end
+
+        it_behaves_like 'tagged build picker'
+      end
+    end
+
+    context 'when runner is locked' do
+      before do
+        runner.locked = true
+      end
+
+      shared_examples 'locked build picker' do
+        context 'when runner cannot pick untagged jobs' do
+          before do
+            runner.run_untagged = false
+          end
+
+          it 'cannot handle builds without tags' do
+            expect(runner.can_pick?(build)).to be_falsey
+          end
+        end
+
+        context 'when having runner tags' do
+          before do
+            runner.tag_list = ['bb', 'cc']
+          end
+
+          it 'cannot handle it for builds without matching tags' do
+            build.tag_list = ['aa']
+
+            expect(runner.can_pick?(build)).to be_falsey
+          end
+        end
+      end
+
+      context 'when serving the same project' do
+        it 'can handle it' do
+          expect(runner.can_pick?(build)).to be_truthy
+        end
+
+        it_behaves_like 'locked build picker'
+
+        context 'when having runner tags' do
+          before do
+            runner.tag_list = ['bb', 'cc']
+            build.tag_list = ['bb']
+          end
+
+          it 'can handle it for matching tags' do
+            expect(runner.can_pick?(build)).to be_truthy
+          end
+        end
+      end
+
+      context 'serving a different project' do
+        before do
+          runner.runner_projects.destroy_all
+        end
+
+        it 'cannot handle it' do
+          expect(runner.can_pick?(build)).to be_falsey
+        end
+
+        it_behaves_like 'locked build picker'
+
+        context 'when having runner tags' do
+          before do
+            runner.tag_list = ['bb', 'cc']
+            build.tag_list = ['bb']
+          end
+
+          it 'cannot handle it for matching tags' do
+            expect(runner.can_pick?(build)).to be_falsey
+          end
+        end
+      end
+    end
+  end
+
+  describe '#status' do
     let(:runner) { FactoryGirl.create(:ci_runner, :shared, contacted_at: 1.second.ago) }
 
     subject { runner.status }
 
     context 'never connected' do
-      before { runner.contacted_at = nil }
+      before do
+        runner.contacted_at = nil
+      end
 
       it { is_expected.to eq(:not_connected) }
     end
 
     context 'contacted 1s ago' do
-      before { runner.contacted_at = 1.second.ago }
+      before do
+        runner.contacted_at = 1.second.ago
+      end
 
       it { is_expected.to eq(:online) }
     end
 
     context 'contacted long time ago' do
-      before { runner.contacted_at = 1.year.ago }
+      before do
+        runner.contacted_at = 1.year.ago
+      end
 
       it { is_expected.to eq(:offline) }
     end
 
     context 'inactive' do
-      before { runner.active = false }
+      before do
+        runner.active = false
+      end
 
       it { is_expected.to eq(:paused) }
     end
   end
 
+  describe '.assignable_for' do
+    let(:runner) { create(:ci_runner) }
+    let(:project) { create(:project) }
+    let(:another_project) { create(:project) }
+
+    before do
+      project.runners << runner
+    end
+
+    context 'with shared runners' do
+      before do
+        runner.update(is_shared: true)
+      end
+
+      context 'does not give owned runner' do
+        subject { Ci::Runner.assignable_for(project) }
+
+        it { is_expected.to be_empty }
+      end
+
+      context 'does not give shared runner' do
+        subject { Ci::Runner.assignable_for(another_project) }
+
+        it { is_expected.to be_empty }
+      end
+    end
+
+    context 'with unlocked runner' do
+      context 'does not give owned runner' do
+        subject { Ci::Runner.assignable_for(project) }
+
+        it { is_expected.to be_empty }
+      end
+
+      context 'does give a specific runner' do
+        subject { Ci::Runner.assignable_for(another_project) }
+
+        it { is_expected.to contain_exactly(runner) }
+      end
+    end
+
+    context 'with locked runner' do
+      before do
+        runner.update(locked: true)
+      end
+
+      context 'does not give owned runner' do
+        subject { Ci::Runner.assignable_for(project) }
+
+        it { is_expected.to be_empty }
+      end
+
+      context 'does not give a locked runner' do
+        subject { Ci::Runner.assignable_for(another_project) }
+
+        it { is_expected.to be_empty }
+      end
+    end
+  end
+
   describe "belongs_to_one_project?" do
     it "returns false if there are two projects runner assigned to" do
       runner = FactoryGirl.create(:ci_runner)
diff --git a/spec/requests/api/runners_spec.rb b/spec/requests/api/runners_spec.rb
index 73ae8ef631c..b4c826522a5 100644
--- a/spec/requests/api/runners_spec.rb
+++ b/spec/requests/api/runners_spec.rb
@@ -187,14 +187,16 @@ describe API::Runners, api: true  do
           update_runner(shared_runner.id, admin, description: "#{description}_updated",
                                                  active: !active,
                                                  tag_list: ['ruby2.1', 'pgsql', 'mysql'],
-                                                 run_untagged: 'false')
+                                                 run_untagged: 'false',
+                                                 locked: 'true')
           shared_runner.reload
 
           expect(response.status).to eq(200)
           expect(shared_runner.description).to eq("#{description}_updated")
           expect(shared_runner.active).to eq(!active)
           expect(shared_runner.tag_list).to include('ruby2.1', 'pgsql', 'mysql')
-          expect(shared_runner.run_untagged?).to be false
+          expect(shared_runner.run_untagged?).to be(false)
+          expect(shared_runner.locked?).to be(true)
         end
       end
 
@@ -360,11 +362,13 @@ describe API::Runners, api: true  do
 
   describe 'POST /projects/:id/runners' do
     context 'authorized user' do
-      it 'should enable specific runner' do
-        specific_runner2 = create(:ci_runner).tap do |runner|
+      let(:specific_runner2) do
+        create(:ci_runner).tap do |runner|
           create(:ci_runner_project, runner: runner, project: project2)
         end
+      end
 
+      it 'should enable specific runner' do
         expect do
           post api("/projects/#{project.id}/runners", user), runner_id: specific_runner2.id
         end.to change{ project.runners.count }.by(+1)
@@ -375,7 +379,17 @@ describe API::Runners, api: true  do
         expect do
           post api("/projects/#{project.id}/runners", user), runner_id: specific_runner.id
         end.to change{ project.runners.count }.by(0)
-        expect(response.status).to eq(201)
+        expect(response.status).to eq(409)
+      end
+
+      it 'should not enable locked runner' do
+        specific_runner2.update(locked: true)
+
+        expect do
+          post api("/projects/#{project.id}/runners", user), runner_id: specific_runner2.id
+        end.to change{ project.runners.count }.by(0)
+
+        expect(response.status).to eq(403)
       end
 
       it 'should not enable shared runner' do