Check Knative installation on cluster

When no deployment has been done yet, there is no environment, so the
check for Knative needs to happen via Kubeclient

app/finders/projects/serverless/functions_finder.rb

@@ -4,9 +4,15 @@ module Projects
   module Serverless
     class FunctionsFinder
       include Gitlab::Utils::StrongMemoize
+      include ReactiveCaching
 
       attr_reader :project
 
+      self.reactive_cache_key = ->(finder) { finder.cache_key }
+      self.reactive_cache_worker_finder = ->(_id, *args) { from_cache(*args) }
+
+      MAX_CLUSTERS = 10
+
       def initialize(project)
         @project = project
       end
@@ -15,8 +21,9 @@ module Projects
         knative_services.flatten.compact
       end
 
-      # Possible return values: Clusters::KnativeServicesFinder::KNATIVE_STATE
       def knative_installed
+        return knative_installed_from_cluster?(*cache_key) if available_environments.empty?
+
         states = services_finders.map do |finder|
           finder.knative_detected.tap do |state|
             return state if state == ::Clusters::KnativeServicesFinder::KNATIVE_STATES['checking'] # rubocop:disable Cop/AvoidReturnFromBlocks
@@ -45,8 +52,41 @@ module Projects
         end
       end
 
+      def self.from_cache(project_id)
+        project = Project.find(project_id)
+
+        new(project)
+      end
+
+      def cache_key(*args)
+        [project.id]
+      end
+
+      def calculate_reactive_cache(*)
+        # rubocop: disable CodeReuse/ActiveRecord
+        project.all_clusters.enabled.take(MAX_CLUSTERS).any? do |cluster|
+          cluster.kubeclient.knative_client.discover
+        rescue Kubeclient::ResourceNotFoundError
+          next
+        end
+      end
+
       private
 
+      def knative_installed_from_cluster?(*cache_key)
+        cached_data = with_reactive_cache_memoized(*cache_key) { |data| data }
+
+        return ::Clusters::KnativeServicesFinder::KNATIVE_STATES['checking'] if cached_data.nil?
+
+        cached_data ? true : false
+      end
+
+      def with_reactive_cache_memoized(*cache_key)
+        strong_memoize(:reactive_cache) do
+          with_reactive_cache(*cache_key) { |data| data }
+        end
+      end
+
       def knative_service(environment_scope, name)
         finders_for_scope(environment_scope).map do |finder|
           services = finder
@@ -95,6 +135,10 @@ module Projects
           environment_scope == finder.cluster.environment_scope
         end
       end
+
+      def id
+        nil
+      end
     end
   end
 end

spec/features/projects/serverless/functions_spec.rb

@@ -16,7 +16,12 @@ describe 'Functions', :js do
 
   shared_examples "it's missing knative installation" do
     before do
+      functions_finder = Projects::Serverless::FunctionsFinder.new(project)
       visit project_serverless_functions_path(project)
+      allow(Projects::Serverless::FunctionsFinder)
+        .to receive(:new)
+        .and_return(functions_finder)
+      synchronous_reactive_cache(functions_finder)
     end
 
     it 'sees an empty state require Knative installation' do

spec/finders/projects/serverless/functions_finder_spec.rb

@@ -26,9 +26,69 @@ describe Projects::Serverless::FunctionsFinder do
     project.add_maintainer(user)
   end
 
-  describe '#installed' do
-    it 'when reactive_caching is still fetching data' do
-      expect(described_class.new(project).knative_installed).to eq 'checking'
+  describe '#knative_installed' do
+    context 'when environment does not exist yet' do
+      shared_examples 'before first deployment' do
+        let(:service) { cluster.platform_kubernetes }
+        let(:deployment) { nil }
+
+        it 'returns true if Knative is installed on cluster' do
+          stub_kubeclient_discover_knative_found(service.api_url)
+          function_finder = described_class.new(project)
+          synchronous_reactive_cache(function_finder)
+
+          expect(function_finder.knative_installed).to be true
+        end
+
+        it 'returns false if Knative is not installed on cluster' do
+          stub_kubeclient_discover_knative_not_found(service.api_url)
+          function_finder = described_class.new(project)
+          synchronous_reactive_cache(function_finder)
+
+          expect(function_finder.knative_installed).to be false
+        end
+      end
+      context 'when project level cluster is present and enabled' do
+        it_behaves_like 'before first deployment' do
+          let(:cluster) { create(:cluster, :project, :provided_by_gcp, enabled: true) }
+          let(:project) { cluster.project }
+        end
+      end
+
+      context 'when group level cluster is present and enabled' do
+        it_behaves_like 'before first deployment' do
+          let(:cluster) { create(:cluster, :group, :provided_by_gcp, enabled: true) }
+          let(:project) { create(:project, group: cluster.groups.first) }
+        end
+      end
+
+      context 'when instance level cluster is present and enabled' do
+        it_behaves_like 'before first deployment' do
+          let(:project) { create(:project) }
+          let(:cluster) { create(:cluster, :instance, :provided_by_gcp, enabled: true) }
+        end
+      end
+
+      context 'when project level cluster is present, but disabled' do
+        let(:cluster) { create(:cluster, :project, :provided_by_gcp, enabled: false) }
+        let(:project) { cluster.project }
+        let(:service) { cluster.platform_kubernetes }
+        let(:deployment) { nil }
+
+        it 'returns false even if Knative is installed on cluster' do
+          stub_kubeclient_discover_knative_found(service.api_url)
+          function_finder = described_class.new(project)
+          synchronous_reactive_cache(function_finder)
+
+          expect(function_finder.knative_installed).to be false
+        end
+      end
+    end
+
+    context 'when reactive_caching is still fetching data' do
+      it 'returns "checking"' do
+        expect(described_class.new(project).knative_installed).to eq 'checking'
+      end
     end
 
     context 'when reactive_caching has finished' do

spec/support/helpers/kubernetes_helpers.rb

@@ -60,6 +60,12 @@ module KubernetesHelpers
       .to_return(status: [404, "Resource Not Found"])
   end
 
+  def stub_kubeclient_discover_knative_found(api_url)
+    WebMock
+      .stub_request(:get, api_url + '/apis/serving.knative.dev/v1alpha1')
+      .to_return(kube_response(kube_knative_discovery_body))
+  end
+
   def stub_kubeclient_service_pods(response = nil, options = {})
     stub_kubeclient_discover(service.api_url)
 
@@ -288,6 +294,13 @@ module KubernetesHelpers
     }
   end
 
+  def kube_knative_discovery_body
+    {
+      "kind" => "APIResourceList",
+      "resources" => []
+    }
+  end
+
   def kube_extensions_v1beta1_discovery_body
     {
       "kind" => "APIResourceList",