Create new projects with prometheus service

When project is created with access to group or instance level k8s
cluster, it has access to applications installed on it. And if
Promethues is among them, it needs to be automatically activated.

app/services/projects/create_service.rb

@@ -98,6 +98,7 @@ module Projects
       setup_authorizations
 
       current_user.invalidate_personal_projects_count
+      create_prometheus_service
 
       create_readme if @initialize_with_readme
     end
@@ -169,6 +170,20 @@ module Projects
     end
     # rubocop: enable CodeReuse/ActiveRecord
 
+    def create_prometheus_service
+      service = @project.find_or_initialize_service(::PrometheusService.to_param)
+
+      if service.prometheus_available?
+        service.save!
+      else
+        @project.prometheus_service = nil
+      end
+
+    rescue ActiveRecord::RecordInvalid => e
+      Gitlab::ErrorTracking.track_exception(e, extra: { project_id: project.id })
+      @project.prometheus_service = nil
+    end
+
     def set_project_name_from_path
       # Set project name from path
       if @project.name.present? && @project.path.present?

changelogs/unreleased/mwaw-activate_shared_services_on_project_creation.yml

+---
+title: Activate Prometheus integration service for newly created project if this project
+  has access to shared Prometheus application.
+merge_request: 24676
+author:
+type: fixed

spec/services/projects/create_service_spec.rb

@@ -344,7 +344,7 @@ describe Projects::CreateService, '#execute' do
 
   context 'when there is an active service template' do
     before do
-      create(:service, project: nil, template: true, active: true)
+      create(:prometheus_service, project: nil, template: true, active: true)
     end
 
     it 'creates a service from this template' do
@@ -394,6 +394,65 @@ describe Projects::CreateService, '#execute' do
     expect(rugged.config['gitlab.fullpath']).to eq project.full_path
   end
 
+  context 'when project has access to shared service' do
+    context 'Prometheus application is shared via group cluster' do
+      let(:cluster) { create(:cluster, :group, groups: [group]) }
+      let(:group) do
+        create(:group).tap do |group|
+          group.add_owner(user)
+        end
+      end
+
+      before do
+        create(:clusters_applications_prometheus, :installed, cluster: cluster)
+      end
+
+      it 'creates PrometheusService record', :aggregate_failures do
+        project = create_project(user, opts.merge!(namespace_id: group.id))
+        service = project.prometheus_service
+        expect(service.active).to be true
+        expect(service.manual_configuration?).to be false
+        expect(service.persisted?).to be true
+      end
+    end
+
+    context 'Prometheus application is shared via instance cluster' do
+      let(:cluster) { create(:cluster, :instance) }
+
+      before do
+        create(:clusters_applications_prometheus, :installed, cluster: cluster)
+      end
+
+      it 'creates PrometheusService record', :aggregate_failures do
+        project = create_project(user, opts)
+        service = project.prometheus_service
+        expect(service.active).to be true
+        expect(service.manual_configuration?).to be false
+        expect(service.persisted?).to be true
+      end
+
+      it 'cleans invalid record and logs warning', :aggregate_failures do
+        invalid_service_record = build(:prometheus_service, properties: { api_url: nil, manual_configuration: true }.to_json)
+        allow_next_instance_of(Project) do |instance|
+          allow(instance).to receive(:build_prometheus_service).and_return(invalid_service_record)
+        end
+
+        expect(Gitlab::ErrorTracking).to receive(:track_exception).with(an_instance_of(ActiveRecord::RecordInvalid), include(extra: { project_id: a_kind_of(Integer) }))
+        project = create_project(user, opts)
+
+        expect(project.prometheus_service).to be_nil
+      end
+    end
+
+    context 'shared Prometheus application is not available' do
+      it 'does not persist PrometheusService record', :aggregate_failures do
+        project = create_project(user, opts)
+        
+        expect(project.prometheus_service).to be_nil
+      end
+    end
+  end
+
   context 'with external authorization enabled' do
     before do
       enable_external_authorization_service_check