Initialize service from instance

find_or_initialize_service has the following precedence:
- Retrieve the existing service
- Build service from instance-level
- Build service from template
- Build service

app/models/project.rb

@@ -1270,12 +1270,18 @@ class Project < ApplicationRecord
     service = find_service(services, name)
     return service if service
 
-    template = find_service(services_templates, name)
+    instance = find_service(services_instances, name)
 
-    if template
-      Service.build_from_integration(id, template)
+    if instance
+      Service.build_from_integration(id, instance)
     else
-      public_send("build_#{name}_service") # rubocop:disable GitlabSecurity/PublicSend
+      template = find_service(services_templates, name)
+
+      if template
+        Service.build_from_integration(id, template)
+      else
+        public_send("build_#{name}_service") # rubocop:disable GitlabSecurity/PublicSend
+      end
     end
   end
 
@@ -2573,7 +2579,11 @@ class Project < ApplicationRecord
   end
 
   def services_templates
-    @services_templates ||= Service.where(template: true)
+    @services_templates ||= Service.templates
+  end
+
+  def services_instances
+    @services_instances ||= Service.instances
   end
 
   def ensure_pages_metadatum

spec/models/project_spec.rb

@@ -5241,12 +5241,10 @@ describe Project do
     end
   end
 
-  describe "#find_or_initialize_services" do
-    subject { build(:project) }
-
+  describe '#find_or_initialize_services' do
     it 'returns only enabled services' do
-      allow(Service).to receive(:available_services_names).and_return(%w(prometheus pushover))
-      allow(subject).to receive(:disabled_services).and_return(%w(prometheus))
+      allow(Service).to receive(:available_services_names).and_return(%w[prometheus pushover])
+      allow(subject).to receive(:disabled_services).and_return(%w[prometheus])
 
       services = subject.find_or_initialize_services
 
@@ -5255,11 +5253,9 @@ describe Project do
     end
   end
 
-  describe "#find_or_initialize_service" do
-    subject { build(:project) }
-
+  describe '#find_or_initialize_service' do
     it 'avoids N+1 database queries' do
-      allow(Service).to receive(:available_services_names).and_return(%w(prometheus pushover))
+      allow(Service).to receive(:available_services_names).and_return(%w[prometheus pushover])
 
       control_count = ActiveRecord::QueryRecorder.new { subject.find_or_initialize_service('prometheus') }.count
 
@@ -5269,10 +5265,36 @@ describe Project do
     end
 
     it 'returns nil if service is disabled' do
-      allow(subject).to receive(:disabled_services).and_return(%w(prometheus))
+      allow(subject).to receive(:disabled_services).and_return(%w[prometheus])
 
       expect(subject.find_or_initialize_service('prometheus')).to be_nil
     end
+
+    it 'builds the service if instance or template does not exists' do
+      expect(subject.find_or_initialize_service('prometheus')).to be_a(PrometheusService)
+      expect(subject.find_or_initialize_service('prometheus').api_url).to be_nil
+    end
+
+    context 'with an instance-level and template integrations' do
+      before do
+        create(:prometheus_service, :instance, api_url: 'https://prometheus.instance.com/')
+        create(:prometheus_service, :template, api_url: 'https://prometheus.template.com/')
+      end
+
+      it 'builds the service from the instance if exists' do
+        expect(subject.find_or_initialize_service('prometheus').api_url).to eq('https://prometheus.instance.com/')
+      end
+    end
+
+    context 'with an instance-level and template integrations' do
+      before do
+        create(:prometheus_service, :template, api_url: 'https://prometheus.template.com/')
+      end
+
+      it 'builds the service from the template if instance does not exists' do
+        expect(subject.find_or_initialize_service('prometheus').api_url).to eq('https://prometheus.template.com/')
+      end
+    end
   end
 
   describe '.for_group' do