Build integration from instance inherits id

Build an integration from an instance-level integration inherits its id.
This is needed in order to propagate the values when the instance-level
settings change.

app/models/service.rb

@@ -355,6 +355,7 @@ class Service < ApplicationRecord
 
     service.template = false
     service.instance = false
+    service.inherit_from_id = integration.id if integration.instance?
     service.project_id = project_id
     service.active = false if service.invalid?
     service

spec/models/service_spec.rb

@@ -279,8 +279,8 @@ describe Service do
     end
 
     describe '.build_from_integration' do
-      context 'when template is invalid' do
-        it 'sets service template to inactive when template is invalid' do
+      context 'when integration is invalid' do
+        it 'sets service to inactive when integration is invalid' do
           template = build(:prometheus_service, template: true, active: true, properties: {})
           template.save(validate: false)
 
@@ -291,7 +291,17 @@ describe Service do
         end
       end
 
-      describe 'build issue tracker from a template' do
+      context 'when integration is an instance' do
+        subject(:integration) { create(:jira_service, :instance) }
+
+        it 'sets service inherit from integration' do
+          service = described_class.build_from_integration(project.id, integration)
+
+          expect(service.inherit_from_id).to eq(integration.id)
+        end
+      end
+
+      describe 'build issue tracker from an integration' do
         let(:title) { 'custom title' }
         let(:description) { 'custom description' }
         let(:url) { 'http://jira.example.com' }
@@ -305,9 +315,9 @@ describe Service do
           }
         end
 
-        shared_examples 'service creation from a template' do
+        shared_examples 'service creation from an integration' do
           it 'creates a correct service' do
-            service = described_class.build_from_integration(project.id, template)
+            service = described_class.build_from_integration(project.id, integration)
 
             expect(service).to be_active
             expect(service.title).to eq(title)
@@ -324,30 +334,30 @@ describe Service do
         # this  will be removed as part of https://gitlab.com/gitlab-org/gitlab/issues/29404
         context 'when data are stored in properties' do
           let(:properties) { data_params.merge(title: title, description: description) }
-          let!(:template) do
+          let!(:integration) do
             create(:jira_service, :without_properties_callback, template: true, properties: properties.merge(additional: 'something'))
           end
 
-          it_behaves_like 'service creation from a template'
+          it_behaves_like 'service creation from an integration'
         end
 
         context 'when data are stored in separated fields' do
-          let(:template) do
+          let(:integration) do
             create(:jira_service, :template, data_params.merge(properties: {}, title: title, description: description))
           end
 
-          it_behaves_like 'service creation from a template'
+          it_behaves_like 'service creation from an integration'
         end
 
         context 'when data are stored in both properties and separated fields' do
           let(:properties) { data_params.merge(title: title, description: description) }
-          let(:template) do
+          let(:integration) do
             create(:jira_service, :without_properties_callback, active: true, template: true, properties: properties).tap do |service|
               create(:jira_tracker_data, data_params.merge(service: service))
             end
           end
 
-          it_behaves_like 'service creation from a template'
+          it_behaves_like 'service creation from an integration'
         end
       end
     end

spec/services/projects/create_service_spec.rb

@@ -453,24 +453,23 @@ describe Projects::CreateService, '#execute' do
     subject(:project) { create_project(user, opts) }
 
     context 'when there is an active instance-level and an active template integration' do
-      before do
-        create(:prometheus_service, :instance, api_url: 'https://prometheus.instance.com/')
-        create(:prometheus_service, :template, api_url: 'https://prometheus.template.com/')
-      end
+      let!(:template_integration) { create(:prometheus_service, :template, api_url: 'https://prometheus.template.com/') }
+      let!(:instance_integration) { create(:prometheus_service, :instance, api_url: 'https://prometheus.instance.com/') }
 
       it 'creates a service from the instance-level integration' do
         expect(project.services.count).to eq(1)
-        expect(project.services.first.api_url).to eq('https://prometheus.instance.com/')
+        expect(project.services.first.api_url).to eq(instance_integration.api_url)
+        expect(project.services.first.inherit_from_id).to eq(instance_integration.id)
       end
     end
 
     context 'when there is an active service template' do
-      before do
-        create(:prometheus_service, :template, active: true)
-      end
+      let!(:template_integration) { create(:prometheus_service, :template, api_url: 'https://prometheus.template.com/') }
 
       it 'creates a service from the template' do
         expect(project.services.count).to eq(1)
+        expect(project.services.first.api_url).to eq(template_integration.api_url)
+        expect(project.services.first.inherit_from_id).to be_nil
       end
     end