Allow setting extra Sentry tags from environment

When GitLab reports an exception from Sentry, it adds tags of
'correlation_id', 'locale', and 'program'. This allows further tags to
be specified by the administrator in the GITLAB_SENTRY_EXTRA_TAGS
environment variable.

This variable must be a JSON-encoded hash of tags to send on every
Sentry event. If it fails to decode from JSON and convert to a hash, it
will simply be empty.

changelogs/unreleased/allow-extra-sentry-tags-from-environment.yml

+---
+title: Allow setting extra tags for Sentry exceptions with GITLAB_SENTRY_EXTRA_TAGS
+merge_request: 35965
+author:
+type: changed

lib/gitlab/error_tracking.rb

@@ -28,7 +28,7 @@ module Gitlab
           config.processors << ::Gitlab::ErrorTracking::Processor::SidekiqProcessor
           # Sanitize authentication headers
           config.sanitize_http_headers = %w[Authorization Private-Token]
-          config.tags = { program: Gitlab.process_name }
+          config.tags = extra_tags_from_env.merge(program: Gitlab.process_name)
           config.before_send = method(:before_send)
 
           yield config if block_given?
@@ -165,6 +165,15 @@ module Gitlab
         }
       end
 
+      # Static tags that are set on application start
+      def extra_tags_from_env
+        Gitlab::Json.parse(ENV.fetch('GITLAB_SENTRY_EXTRA_TAGS', '{}')).to_hash
+      rescue => e
+        Gitlab::AppLogger.debug("GITLAB_SENTRY_EXTRA_TAGS could not be parsed as JSON: #{e.class.name}: #{e.message}")
+
+        {}
+      end
+
       # Debugging for https://gitlab.com/gitlab-org/gitlab-foss/issues/57727
       def add_context_from_exception_type(event, hint)
         if ActiveModel::MissingAttributeError === hint[:exception]

spec/lib/gitlab/error_tracking_spec.rb

@@ -18,6 +18,8 @@ RSpec.describe Gitlab::ErrorTracking do
     ]
   end
 
+  let(:sentry_event) { Gitlab::Json.parse(Raven.client.transport.events.last[1]) }
+
   before do
     stub_sentry_settings
 
@@ -29,6 +31,86 @@ RSpec.describe Gitlab::ErrorTracking do
     end
   end
 
+  describe '.configure' do
+    context 'default tags from GITLAB_SENTRY_EXTRA_TAGS' do
+      context 'when the value is a JSON hash' do
+        it 'includes those tags in all events' do
+          stub_env('GITLAB_SENTRY_EXTRA_TAGS', { foo: 'bar', baz: 'quux' }.to_json)
+
+          described_class.configure do |config|
+            config.encoding = 'json'
+          end
+
+          described_class.track_exception(StandardError.new)
+
+          expect(sentry_event['tags'].except('correlation_id', 'locale', 'program'))
+            .to eq('foo' => 'bar', 'baz' => 'quux')
+        end
+      end
+
+      context 'when the value is not set' do
+        before do
+          stub_env('GITLAB_SENTRY_EXTRA_TAGS', nil)
+        end
+
+        it 'does not log an error' do
+          expect(Gitlab::AppLogger).not_to receive(:debug)
+
+          described_class.configure do |config|
+            config.encoding = 'json'
+          end
+        end
+
+        it 'does not send any extra tags' do
+          described_class.configure do |config|
+            config.encoding = 'json'
+          end
+
+          described_class.track_exception(StandardError.new)
+
+          expect(sentry_event['tags'].keys).to contain_exactly('correlation_id', 'locale', 'program')
+        end
+      end
+
+      context 'when the value is not a JSON hash' do
+        using RSpec::Parameterized::TableSyntax
+
+        where(:env_var, :error) do
+          { foo: 'bar', baz: 'quux' }.inspect | 'JSON::ParserError'
+          [].to_json | 'NoMethodError'
+          [%w[foo bar]].to_json | 'NoMethodError'
+          %w[foo bar].to_json | 'NoMethodError'
+          '"string"' | 'NoMethodError'
+        end
+
+        with_them do
+          before do
+            stub_env('GITLAB_SENTRY_EXTRA_TAGS', env_var)
+          end
+
+          it 'does not include any extra tags' do
+            described_class.configure do |config|
+              config.encoding = 'json'
+            end
+
+            described_class.track_exception(StandardError.new)
+
+            expect(sentry_event['tags'].except('correlation_id', 'locale', 'program'))
+              .to be_empty
+          end
+
+          it 'logs the error class' do
+            expect(Gitlab::AppLogger).to receive(:debug).with(a_string_matching(error))
+
+            described_class.configure do |config|
+              config.encoding = 'json'
+            end
+          end
+        end
+      end
+    end
+  end
+
   describe '.with_context' do
     it 'adds the expected tags' do
       described_class.with_context {}
@@ -202,8 +284,6 @@ RSpec.describe Gitlab::ErrorTracking do
 
         described_class.track_exception(exception, extra)
 
-        sentry_event = Gitlab::Json.parse(Raven.client.transport.events.last[1])
-
         expect(sentry_event.dig('extra', 'sidekiq', 'args')).to eq(['[FILTERED]', 1, 2])
       end
     end