Allow disabling usage ping in `gitlab.yml`

Setting `usage_ping_enabled` to false in `gitlab.yml`:

1. Disables the usage ping, regardless of the value stored in the database.
2. Prevents the usage ping from being enabled through the admin panel. It can
   only be enabled by either removing the line from `gitlab.yml` and configuring
   through the admin panel, or setting it to true in `gitlab.yml`.

app/models/application_setting.rb

@@ -246,7 +246,7 @@ class ApplicationSetting < ActiveRecord::Base
       two_factor_grace_period: 48,
       user_default_external: false,
       polling_interval_multiplier: 1,
-      usage_ping_enabled: true
+      usage_ping_enabled: Settings.gitlab['usage_ping_enabled']
     }
   end
 
@@ -349,6 +349,14 @@ class ApplicationSetting < ActiveRecord::Base
     sidekiq_throttling_enabled
   end
 
+  def usage_ping_can_be_configured?
+    Settings.gitlab.usage_ping_enabled
+  end
+
+  def usage_ping_enabled
+    usage_ping_can_be_configured? && super
+  end
+
   private
 
   def ensure_uuid!

app/views/admin/application_settings/_form.html.haml

@@ -502,17 +502,24 @@
             Let GitLab inform you when an update is available.
     .form-group
       .col-sm-offset-2.col-sm-10
+        - can_be_configured = @application_setting.usage_ping_can_be_configured?
         .checkbox
           = f.label :usage_ping_enabled do
-            = f.check_box :usage_ping_enabled
+            = f.check_box :usage_ping_enabled, disabled: !can_be_configured
             Usage ping enabled
-            = link_to icon('question-circle'), help_page_path("user/admin_area/settings/usage_statistics", anchor: "usage-data")
+            = link_to icon('question-circle'), help_page_path("user/admin_area/settings/usage_statistics", anchor: "usage-ping")
           .help-block
+            - if can_be_configured
               Every week GitLab will report license usage back to GitLab, Inc.
               Disable this option if you do not want this to occur. To see the
               JSON payload that will be sent, visit the
               = succeed '.' do
                 = link_to "Cohorts page", admin_cohorts_path(anchor: 'usage-ping')
+            - else
+              The usage ping is disabled, and cannot be configured through this
+              form. For more information, see the documentation on
+              = succeed '.' do
+                = link_to 'deactivating the usage ping', help_page_path('user/admin_area/settings/usage_statistics', anchor: 'deactivate-the-usage-ping')
 
   %fieldset
     %legend Email

changelogs/unreleased/disable-usage-ping.yml

+---
+title: Allow usage ping to be disabled completely in gitlab.yml
+merge_request:
+author:

config/initializers/1_settings.rb

@@ -241,6 +241,7 @@ Settings.gitlab['domain_whitelist'] ||= []
 Settings.gitlab['import_sources'] ||= %w[github bitbucket gitlab google_code fogbugz git gitlab_project gitea]
 Settings.gitlab['trusted_proxies'] ||= []
 Settings.gitlab['no_todos_messages'] ||= YAML.load_file(Rails.root.join('config', 'no_todos_messages.yml'))
+Settings.gitlab['usage_ping_enabled'] = true if Settings.gitlab['usage_ping_enabled'].nil?
 
 #
 # CI

doc/user/admin_area/settings/usage_statistics.md

@@ -89,6 +89,24 @@ By default, usage ping is opt-out. If you want to deactivate this feature, go to
 the Settings page of your administration panel and uncheck the Usage ping
 checkbox.
 
+To disable the usage ping and prevent it from being configured from the
+administration panel, Omnibus installs can set the following in
+[`gitlab.rb`](https://docs.gitlab.com/omnibus/settings/configuration.html#configuration-options):
+
+```ruby
+gitlab_rails['usage_ping_enabled'] = false
+```
+
+And source installs can set the following in `gitlab.yml`:
+
+```yaml
+production: &base
+  # ...
+  gitlab:
+    # ...
+    usage_ping_enabled: false
+```
+
 ## Privacy policy
 
 GitLab Inc. does **not** collect any sensitive information, like project names

spec/models/application_setting_spec.rb

@@ -211,4 +211,66 @@ describe ApplicationSetting, models: true do
       expect(setting.domain_blacklist).to contain_exactly('example.com', 'test.com', 'foo.bar')
     end
   end
+
+  describe 'usage ping settings' do
+    context 'when the usage ping is disabled in gitlab.yml' do
+      before do
+        allow(Settings.gitlab).to receive(:usage_ping_enabled).and_return(false)
+      end
+
+      it 'does not allow the usage ping to be configured' do
+        expect(setting.usage_ping_can_be_configured?).to be_falsey
+      end
+
+      context 'when the usage ping is disabled in the DB' do
+        before do
+          setting.usage_ping_enabled = false
+        end
+
+        it 'returns false for usage_ping_enabled' do
+          expect(setting.usage_ping_enabled).to be_falsey
+        end
+      end
+
+      context 'when the usage ping is enabled in the DB' do
+        before do
+          setting.usage_ping_enabled = true
+        end
+
+        it 'returns false for usage_ping_enabled' do
+          expect(setting.usage_ping_enabled).to be_falsey
+        end
+      end
+    end
+
+    context 'when the usage ping is enabled in gitlab.yml' do
+      before do
+        allow(Settings.gitlab).to receive(:usage_ping_enabled).and_return(true)
+      end
+
+      it 'allows the usage ping to be configured' do
+        expect(setting.usage_ping_can_be_configured?).to be_truthy
+      end
+
+      context 'when the usage ping is disabled in the DB' do
+        before do
+          setting.usage_ping_enabled = false
+        end
+
+        it 'returns false for usage_ping_enabled' do
+          expect(setting.usage_ping_enabled).to be_falsey
+        end
+      end
+
+      context 'when the usage ping is enabled in the DB' do
+        before do
+          setting.usage_ping_enabled = true
+        end
+
+        it 'returns true for usage_ping_enabled' do
+          expect(setting.usage_ping_enabled).to be_truthy
+        end
+      end
+    end
+  end
 end