Add reactive caching worker for external services

Introduces a separated worker to handle reactive caching
that performs external requests.

This worker needs to stay in lower priority given it's
not possible to predict how external services will perform.
I.e. this work should not block other work with higher
priority.

app/models/concerns/reactive_caching.rb

@@ -8,6 +8,11 @@ module ReactiveCaching
   InvalidateReactiveCache = Class.new(StandardError)
   ExceededReactiveCacheLimit = Class.new(StandardError)
 
+  WORK_TYPE = {
+    default: ReactiveCachingWorker,
+    external_dependency: ExternalServiceReactiveCachingWorker
+  }.freeze
+
   included do
     extend ActiveModel::Naming
 
@@ -16,6 +21,7 @@ module ReactiveCaching
     class_attribute :reactive_cache_refresh_interval
     class_attribute :reactive_cache_lifetime
     class_attribute :reactive_cache_hard_limit
+    class_attribute :reactive_cache_work_type
     class_attribute :reactive_cache_worker_finder
 
     # defaults
@@ -24,6 +30,7 @@ module ReactiveCaching
     self.reactive_cache_refresh_interval = 1.minute
     self.reactive_cache_lifetime = 10.minutes
     self.reactive_cache_hard_limit = 1.megabyte
+    self.reactive_cache_work_type = :default
     self.reactive_cache_worker_finder = ->(id, *_args) do
       find_by(primary_key => id)
     end
@@ -112,7 +119,7 @@ module ReactiveCaching
     def refresh_reactive_cache!(*args)
       clear_reactive_cache!(*args)
       keep_alive_reactive_cache!(*args)
-      ReactiveCachingWorker.perform_async(self.class, id, *args)
+      worker_class.perform_async(self.class, id, *args)
     end
 
     def keep_alive_reactive_cache!(*args)
@@ -145,7 +152,11 @@ module ReactiveCaching
     def enqueuing_update(*args)
       yield
 
-      ReactiveCachingWorker.perform_in(self.class.reactive_cache_refresh_interval, self.class, id, *args)
+      worker_class.perform_in(self.class.reactive_cache_refresh_interval, self.class, id, *args)
+    end
+
+    def worker_class
+      WORK_TYPE.fetch(self.class.reactive_cache_work_type.to_sym)
     end
 
     def check_exceeded_reactive_cache_limit!(data)

app/workers/all_queues.yml

@@ -1060,6 +1060,13 @@
   :resource_boundary: :cpu
   :weight: 1
   :idempotent: 
+- :name: external_service_reactive_caching
+  :feature_category: :not_owned
+  :has_external_dependencies: true
+  :urgency: :low
+  :resource_boundary: :unknown
+  :weight: 1
+  :idempotent: 
 - :name: file_hook
   :feature_category: :integrations
   :has_external_dependencies: 

app/workers/concerns/reactive_cacheable_worker.rb

+# frozen_string_literal: true
+
+module ReactiveCacheableWorker
+  extend ActiveSupport::Concern
+
+  included do
+    include ApplicationWorker
+
+    feature_category_not_owned!
+
+    def self.context_for_arguments(arguments)
+      class_name, *_other_args = arguments
+      Gitlab::ApplicationContext.new(related_class: class_name.to_s)
+    end
+  end
+
+  def perform(class_name, id, *args)
+    klass = begin
+              class_name.constantize
+            rescue NameError
+              nil
+            end
+
+    return unless klass
+
+    klass
+      .reactive_cache_worker_finder
+      .call(id, *args)
+      .try(:exclusively_update_reactive_cache!, *args)
+  rescue ReactiveCaching::ExceededReactiveCacheLimit => e
+    Gitlab::ErrorTracking.track_exception(e)
+  end
+end

app/workers/external_service_reactive_caching_worker.rb

+# frozen_string_literal: true
+
+class ExternalServiceReactiveCachingWorker # rubocop:disable Scalability/IdempotentWorker
+  include ReactiveCacheableWorker
+
+  worker_has_external_dependencies!
+end

app/workers/reactive_caching_worker.rb

 # frozen_string_literal: true
 
 class ReactiveCachingWorker # rubocop:disable Scalability/IdempotentWorker
-  include ApplicationWorker
+  include ReactiveCacheableWorker
 
-  feature_category_not_owned!
-
-  # TODO: The reactive caching worker should be split into
-  # two different workers, one for high urgency jobs without external dependencies
-  # and another worker without high urgency, but with external dependencies
-  # https://gitlab.com/gitlab-com/gl-infra/scalability/issues/34
-  # This worker should also have `worker_has_external_dependencies!` enabled
   urgency :high
   worker_resource_boundary :cpu
-
-  def self.context_for_arguments(arguments)
-    class_name, *_other_args = arguments
-    Gitlab::ApplicationContext.new(related_class: class_name.to_s)
-  end
-
-  def perform(class_name, id, *args)
-    klass = begin
-      class_name.constantize
-    rescue NameError
-      nil
-    end
-    return unless klass
-
-    klass
-      .reactive_cache_worker_finder
-      .call(id, *args)
-      .try(:exclusively_update_reactive_cache!, *args)
-  rescue ReactiveCaching::ExceededReactiveCacheLimit => e
-    Gitlab::ErrorTracking.track_exception(e)
-  end
 end

config/sidekiq_queues.yml

@@ -100,6 +100,8 @@
   - 1
 - - export_csv
   - 1
+- - external_service_reactive_caching
+  - 1
 - - file_hook
   - 1
 - - gcp_cluster

doc/development/reactive_caching.md

@@ -85,6 +85,9 @@ The ReactiveCaching concern can be used in models as well as `project_services`
 
 1. Implement the `calculate_reactive_cache` method in your model/service.
 1. Call `with_reactive_cache` in your model/service where the cached value is needed.
+1. If the `calculate_reactive_cache` method above submits requests to external services
+(e.g. Prometheus, K8s), make sure to change the
+[`reactive_cache_work_type` accordingly](#selfreactive_cache_work_type).
 
 ### In controllers
 
@@ -244,6 +247,13 @@ and will silently raise `ReactiveCaching::ExceededReactiveCacheLimit` on Sentry.
 self.reactive_cache_hard_limit = 5.megabytes
 ```
 
+#### `self.reactive_cache_work_type`
+
+- This is the type of work performed by the `calculate_reactive_cache` method. Based on this attribute,
+it's able to pick the right worker to process the caching job. Make sure to
+set it as `:external_dependency` if the work performs any external request
+(e.g. Kubernetes, Sentry).
+
 #### `self.reactive_cache_worker_finder`
 
 - This is the method used by the background worker to find or generate the object on

spec/models/concerns/reactive_caching_spec.rb

@@ -6,7 +6,8 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
   include ExclusiveLeaseHelpers
   include ReactiveCachingHelpers
 
-  class CacheTest
+  let(:cache_class_test) do
+    Class.new do
       include ReactiveCaching
 
       self.reactive_cache_key = ->(thing) { ["foo", thing.id] }
@@ -35,10 +36,17 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
         end
       end
     end
+  end
+
+  let(:external_dependency_cache_class_test) do
+    Class.new(cache_class_test) do
+      self.reactive_cache_work_type = :external_dependency
+    end
+  end
 
   let(:calculation) { -> { 2 + 2 } }
   let(:cache_key) { "foo:666" }
-  let(:instance) { CacheTest.new(666, &calculation) }
+  let(:instance) { cache_class_test.new(666, &calculation) }
 
   describe '#with_reactive_cache' do
     before do
@@ -47,6 +55,18 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
 
     subject(:go!) { instance.result }
 
+    shared_examples 'reactive worker call' do |worker_class|
+      let(:instance) do
+        test_class.new(666, &calculation)
+      end
+
+      it 'performs caching with correct worker' do
+        expect(worker_class).to receive(:perform_async).with(test_class, 666)
+
+        go!
+      end
+    end
+
     shared_examples 'a cacheable value' do |cached_value|
       before do
         stub_reactive_cache(instance, cached_value)
@@ -73,10 +93,12 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
 
         it { is_expected.to be_nil }
 
-        it 'refreshes cache' do
-          expect(ReactiveCachingWorker).to receive(:perform_async).with(CacheTest, 666)
+        it_behaves_like 'reactive worker call', ReactiveCachingWorker do
+          let(:test_class) { cache_class_test }
+        end
 
-          instance.with_reactive_cache { raise described_class::InvalidateReactiveCache }
+        it_behaves_like 'reactive worker call', ExternalServiceReactiveCachingWorker do
+          let(:test_class) { external_dependency_cache_class_test }
         end
       end
     end
@@ -84,10 +106,12 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
     context 'when cache is empty' do
       it { is_expected.to be_nil }
 
-      it 'enqueues a background worker to bootstrap the cache' do
-        expect(ReactiveCachingWorker).to receive(:perform_async).with(CacheTest, 666)
+      it_behaves_like 'reactive worker call', ReactiveCachingWorker do
+        let(:test_class) { cache_class_test }
+      end
 
-        go!
+      it_behaves_like 'reactive worker call', ExternalServiceReactiveCachingWorker do
+        let(:test_class) { external_dependency_cache_class_test }
       end
 
       it 'updates the cache lifespan' do
@@ -168,13 +192,15 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
 
     context 'with custom reactive_cache_worker_finder' do
       let(:args) { %w(arg1 arg2) }
-      let(:instance) { CustomFinderCacheTest.new(666, &calculation) }
+      let(:instance) { custom_finder_cache_test.new(666, &calculation) }
 
-      class CustomFinderCacheTest < CacheTest
+      let(:custom_finder_cache_test) do
+        Class.new(cache_class_test) do
           self.reactive_cache_worker_finder = ->(_id, *args) { from_cache(*args) }
 
           def self.from_cache(*args); end
         end
+      end
 
       before do
         allow(instance.class).to receive(:from_cache).with(*args).and_return(instance)
@@ -234,6 +260,18 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
         go!
       end
 
+      context 'when :external_dependency cache' do
+        let(:instance) do
+          external_dependency_cache_class_test.new(666, &calculation)
+        end
+
+        it 'enqueues a repeat worker' do
+          expect_reactive_cache_update_queued(instance, worker_klass: ExternalServiceReactiveCachingWorker)
+
+          go!
+        end
+      end
+
       it 'calls a reactive_cache_updated only once if content did not change on subsequent update' do
         expect(instance).to receive(:calculate_reactive_cache).twice
         expect(instance).to receive(:reactive_cache_updated).once
@@ -262,7 +300,7 @@ describe ReactiveCaching, :use_clean_rails_memory_store_caching do
           it_behaves_like 'ExceededReactiveCacheLimit'
 
           context 'when reactive_cache_hard_limit is overridden' do
-            let(:test_class) { Class.new(CacheTest) { self.reactive_cache_hard_limit = 3.megabytes } }
+            let(:test_class) { Class.new(cache_class_test) { self.reactive_cache_hard_limit = 3.megabytes } }
             let(:instance) { test_class.new(666, &calculation) }
 
             it_behaves_like 'successful cache'

spec/support/helpers/reactive_caching_helpers.rb

@@ -10,8 +10,11 @@ module ReactiveCachingHelpers
   end
 
   def stub_reactive_cache(subject = nil, data = nil, *qualifiers)
-    allow(ReactiveCachingWorker).to receive(:perform_async)
-    allow(ReactiveCachingWorker).to receive(:perform_in)
+    ReactiveCaching::WORK_TYPE.values.each do |worker|
+      allow(worker).to receive(:perform_async)
+      allow(worker).to receive(:perform_in)
+    end
+
     write_reactive_cache(subject, data, *qualifiers) unless subject.nil?
   end
 
@@ -42,8 +45,8 @@ module ReactiveCachingHelpers
     Rails.cache.write(alive_reactive_cache_key(subject, *qualifiers), true)
   end
 
-  def expect_reactive_cache_update_queued(subject)
-    expect(ReactiveCachingWorker)
+  def expect_reactive_cache_update_queued(subject, worker_klass: ReactiveCachingWorker)
+    expect(worker_klass)
       .to receive(:perform_in)
       .with(subject.class.reactive_cache_refresh_interval, subject.class, subject.id)
   end

spec/support/shared_examples/workers/reactive_cacheable_shared_examples.rb

+# frozen_string_literal: true
+
+RSpec.shared_examples 'reactive cacheable worker' do
+  describe '#perform' do
+    context 'when reactive cache worker class is found' do
+      let!(:cluster) { create(:cluster, :project, :provided_by_gcp) }
+      let(:project) { cluster.project }
+      let!(:environment) { create(:environment, project: project) }
+
+      it 'calls #exclusively_update_reactive_cache!' do
+        expect_any_instance_of(Environment).to receive(:exclusively_update_reactive_cache!)
+
+        described_class.new.perform("Environment", environment.id)
+      end
+
+      context 'when ReactiveCaching::ExceededReactiveCacheLimit is raised' do
+        it 'avoids failing the job and tracks via Gitlab::ErrorTracking' do
+          allow_any_instance_of(Environment).to receive(:exclusively_update_reactive_cache!)
+            .and_raise(ReactiveCaching::ExceededReactiveCacheLimit)
+
+          expect(Gitlab::ErrorTracking).to receive(:track_exception)
+            .with(kind_of(ReactiveCaching::ExceededReactiveCacheLimit))
+
+          described_class.new.perform("Environment", environment.id)
+        end
+      end
+    end
+
+    context 'when reactive cache worker class is not found' do
+      it 'raises no error' do
+        expect { described_class.new.perform("Environment", -1) }.not_to raise_error
+      end
+    end
+
+    context 'when reactive cache worker class is invalid' do
+      it 'raises no error' do
+        expect { described_class.new.perform("FooBarKux", -1) }.not_to raise_error
+      end
+    end
+  end
+
+  describe 'worker context' do
+    it 'sets the related class on the job' do
+      described_class.perform_async('Environment', 1, 'other', 'argument')
+
+      scheduled_job = described_class.jobs.first
+
+      expect(scheduled_job).to include('meta.related_class' => 'Environment')
+    end
+
+    it 'sets the related class on the job when it was passed as a class' do
+      described_class.perform_async(Project, 1, 'other', 'argument')
+
+      scheduled_job = described_class.jobs.first
+
+      expect(scheduled_job).to include('meta.related_class' => 'Project')
+    end
+  end
+end

spec/workers/external_service_reactive_caching_worker_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ExternalServiceReactiveCachingWorker do
+  it_behaves_like 'reactive cacheable worker'
+end

spec/workers/reactive_caching_worker_spec.rb

@@ -3,47 +3,5 @@
 require 'spec_helper'
 
 describe ReactiveCachingWorker do
-  describe '#perform' do
-    context 'when user configured kubernetes from CI/CD > Clusters' do
-      let!(:cluster) { create(:cluster, :project, :provided_by_gcp) }
-      let(:project) { cluster.project }
-      let!(:environment) { create(:environment, project: project) }
-
-      it 'calls #exclusively_update_reactive_cache!' do
-        expect_any_instance_of(Environment).to receive(:exclusively_update_reactive_cache!)
-
-        described_class.new.perform("Environment", environment.id)
-      end
-
-      context 'when ReactiveCaching::ExceededReactiveCacheLimit is raised' do
-        it 'avoids failing the job and tracks via Gitlab::ErrorTracking' do
-          allow_any_instance_of(Environment).to receive(:exclusively_update_reactive_cache!)
-            .and_raise(ReactiveCaching::ExceededReactiveCacheLimit)
-
-          expect(Gitlab::ErrorTracking).to receive(:track_exception)
-            .with(kind_of(ReactiveCaching::ExceededReactiveCacheLimit))
-
-          described_class.new.perform("Environment", environment.id)
-        end
-      end
-    end
-  end
-
-  describe 'worker context' do
-    it 'sets the related class on the job' do
-      described_class.perform_async('Environment', 1, 'other', 'argument')
-
-      scheduled_job = described_class.jobs.first
-
-      expect(scheduled_job).to include('meta.related_class' => 'Environment')
-    end
-
-    it 'sets the related class on the job when it was passed as a class' do
-      described_class.perform_async(Project, 1, 'other', 'argument')
-
-      scheduled_job = described_class.jobs.first
-
-      expect(scheduled_job).to include('meta.related_class' => 'Project')
-    end
-  end
+  it_behaves_like 'reactive cacheable worker'
 end