Allow knative do be uninstalled:

- After uninstalling the knative helm chart it's necessary to also
remove some leftover resources to allow the cluster to be clean
and knative to be reinstalleable.
- Adds knative uninstall disclaimer
- Uninstall ksvc before uninstalling knative

Make list of Knative and Ingres resources explicit

- To avoid deleting unwanted resources we are listing exact
which resources will be deleted rather than simply deleting any
resource that contains istio or knative words.

13 files changed, 188 insertions, 24 deletions

diff --git a/app/assets/javascripts/clusters/components/uninstall_application_confirmation_modal.vue b/app/assets/javascripts/clusters/components/uninstall_application_confirmation_modal.vue
index 920439ebb23..2ff6d5e32e2 100644
--- a/app/assets/javascripts/clusters/components/uninstall_application_confirmation_modal.vue
+++ b/app/assets/javascripts/clusters/components/uninstall_application_confirmation_modal.vue
@@ -13,7 +13,9 @@ const CUSTOM_APP_WARNING_TEXT = {
   ),
   [PROMETHEUS]: s__('ClusterIntegration|All data will be deleted and cannot be restored.'),
   [RUNNER]: s__('ClusterIntegration|Any running pipelines will be canceled.'),
-  [KNATIVE]: s__('ClusterIntegration|The associated IP will be deleted and cannot be restored.'),
+  [KNATIVE]: s__(
+    'ClusterIntegration|The associated IP and all deployed services will be deleted and cannot be restored. Uninstalling Knative will also remove Istio from your cluster. This will not effect any other applications.',
+  ),
   [JUPYTER]: s__(
     'ClusterIntegration|All data not committed to GitLab will be deleted and cannot be restored.',
   ),
diff --git a/app/models/clusters/applications/cert_manager.rb b/app/models/clusters/applications/cert_manager.rb
index d6a7d1d2bdd..7d5a6dec519 100644
--- a/app/models/clusters/applications/cert_manager.rb
+++ b/app/models/clusters/applications/cert_manager.rb
@@ -44,7 +44,7 @@ module Clusters
       private
 
       def post_install_script
-        ["/usr/bin/kubectl create -f /data/helm/certmanager/config/cluster_issuer.yaml"]
+        ["kubectl create -f /data/helm/certmanager/config/cluster_issuer.yaml"]
       end
 
       def cluster_issuer_file
diff --git a/app/models/clusters/applications/knative.rb b/app/models/clusters/applications/knative.rb
index 5df4812bd25..96f526e8a36 100644
--- a/app/models/clusters/applications/knative.rb
+++ b/app/models/clusters/applications/knative.rb
@@ -7,6 +7,7 @@ module Clusters
       REPOSITORY = 'https://storage.googleapis.com/triggermesh-charts'.freeze
       METRICS_CONFIG = 'https://storage.googleapis.com/triggermesh-charts/istio-metrics.yaml'.freeze
       FETCH_IP_ADDRESS_DELAY = 30.seconds
+      API_RESOURCES_PATH = 'config/knative/api_resources.yml'
 
       self.table_name = 'clusters_applications_knative'
 
@@ -46,12 +47,6 @@ module Clusters
         { "domain" => hostname }.to_yaml
       end
 
-      # Handled in a new issue:
-      # https://gitlab.com/gitlab-org/gitlab-ce/issues/59369
-      def allowed_to_uninstall?
-        false
-      end
-
       def install_command
         Gitlab::Kubernetes::Helm::InstallCommand.new(
           name: name,
@@ -76,12 +71,59 @@ module Clusters
         cluster.kubeclient.get_service('istio-ingressgateway', 'istio-system')
       end
 
+      def uninstall_command
+        Gitlab::Kubernetes::Helm::DeleteCommand.new(
+          name: name,
+          rbac: cluster.platform_kubernetes_rbac?,
+          files: files,
+          predelete: delete_knative_services_and_metrics,
+          postdelete: delete_knative_istio_leftovers
+        )
+      end
+
       private
 
+      def delete_knative_services_and_metrics
+        delete_knative_services + delete_knative_istio_metrics.to_a
+      end
+
+      def delete_knative_services
+        cluster.kubernetes_namespaces.map do |kubernetes_namespace|
+          "kubectl delete ksvc --all -n #{kubernetes_namespace.namespace}"
+        end
+      end
+
+      def delete_knative_istio_leftovers
+        delete_knative_namespaces + delete_knative_and_istio_crds
+      end
+
+      def delete_knative_namespaces
+        [
+          "kubectl delete --ignore-not-found ns knative-serving",
+          "kubectl delete --ignore-not-found ns knative-build"
+        ]
+      end
+
+      def delete_knative_and_istio_crds
+        api_resources.map do |crd|
+          "kubectl delete --ignore-not-found crd #{crd}"
+        end
+      end
+
+      # returns an array of CRDs to be postdelete since helm does not
+      # manage the CRDs it creates.
+      def api_resources
+        @api_resources ||= YAML.safe_load(File.read(Rails.root.join(API_RESOURCES_PATH)))
+      end
+
       def install_knative_metrics
         ["kubectl apply -f #{METRICS_CONFIG}"] if cluster.application_prometheus_available?
       end
 
+      def delete_knative_istio_metrics
+        ["kubectl delete --ignore-not-found -f #{METRICS_CONFIG}"] if cluster.application_prometheus_available?
+      end
+
       def verify_cluster?
         cluster&.application_helm_available? && cluster&.platform_kubernetes_rbac?
       end
diff --git a/app/models/clusters/applications/prometheus.rb b/app/models/clusters/applications/prometheus.rb
index 805c8a73f8c..f5375d29f3a 100644
--- a/app/models/clusters/applications/prometheus.rb
+++ b/app/models/clusters/applications/prometheus.rb
@@ -59,6 +59,15 @@ module Clusters
         )
       end
 
+      def uninstall_command
+        Gitlab::Kubernetes::Helm::DeleteCommand.new(
+          name: name,
+          rbac: cluster.platform_kubernetes_rbac?,
+          files: files,
+          predelete: delete_knative_istio_metrics.to_a
+        )
+      end
+
       # Returns a copy of files where the values of 'values.yaml'
       # are replaced by the argument.
       #
@@ -97,6 +106,10 @@ module Clusters
       def install_knative_metrics
         ["kubectl apply -f #{Clusters::Applications::Knative::METRICS_CONFIG}"] if cluster.application_knative_available?
       end
+
+      def delete_knative_istio_metrics
+        ["kubectl delete -f #{Clusters::Applications::Knative::METRICS_CONFIG}"] if cluster.application_knative_available?
+      end
     end
   end
 end
diff --git a/changelogs/unreleased/60668-kubernetes-applications-uninstall-knative.yml b/changelogs/unreleased/60668-kubernetes-applications-uninstall-knative.yml
new file mode 100644
index 00000000000..c33dc0f50cd
--- /dev/null
+++ b/changelogs/unreleased/60668-kubernetes-applications-uninstall-knative.yml
@@ -0,0 +1,5 @@
+---
+title: Allow Knative to be uninstalled from the UI
+merge_request: 30458
+author:
+type: added
diff --git a/config/knative/api_resources.yml b/config/knative/api_resources.yml
new file mode 100644
index 00000000000..43427b730db
--- /dev/null
+++ b/config/knative/api_resources.yml
@@ -0,0 +1,64 @@
+---
+
+- meshpolicies.authentication.istio.io
+- policies.authentication.istio.io
+- adapters.config.istio.io
+- apikeys.config.istio.io
+- attributemanifests.config.istio.io
+- authorizations.config.istio.io
+- bypasses.config.istio.io
+- podautoscalers.autoscaling.internal.knative.dev
+- builds.build.knative.dev
+- buildtemplates.build.knative.dev
+- clusterbuildtemplates.build.knative.dev
+- images.caching.internal.knative.dev
+- certificates.networking.internal.knative.dev
+- clusteringresses.networking.internal.knative.dev
+- serverlessservices.networking.internal.knative.dev
+- configurations.serving.knative.dev
+- revisions.serving.knative.dev
+- routes.serving.knative.dev
+- services.serving.knative.dev
+- checknothings.config.istio.io
+- circonuses.config.istio.io
+- deniers.config.istio.io
+- edges.config.istio.io
+- fluentds.config.istio.io
+- handlers.config.istio.io
+- httpapispecbindings.config.istio.io
+- httpapispecs.config.istio.io
+- instances.config.istio.io
+- kubernetesenvs.config.istio.io
+- kuberneteses.config.istio.io
+- listcheckers.config.istio.io
+- listentries.config.istio.io
+- logentries.config.istio.io
+- memquotas.config.istio.io
+- metrics.config.istio.io
+- noops.config.istio.io
+- opas.config.istio.io
+- prometheuses.config.istio.io
+- quotas.config.istio.io
+- quotaspecbindings.config.istio.io
+- quotaspecs.config.istio.io
+- rbacs.config.istio.io
+- redisquotas.config.istio.io
+- reportnothings.config.istio.io
+- rules.config.istio.io
+- servicecontrolreports.config.istio.io
+- servicecontrols.config.istio.io
+- signalfxs.config.istio.io
+- solarwindses.config.istio.io
+- stackdrivers.config.istio.io
+- statsds.config.istio.io
+- stdios.config.istio.io
+- templates.config.istio.io
+- tracespans.config.istio.io
+- destinationrules.networking.istio.io
+- envoyfilters.networking.istio.io
+- gateways.networking.istio.io
+- serviceentries.networking.istio.io
+- virtualservices.networking.istio.io
+- rbacconfigs.rbac.istio.io
+- servicerolebindings.rbac.istio.io
+- serviceroles.rbac.istio.io
\ No newline at end of file
diff --git a/doc/user/clusters/applications.md b/doc/user/clusters/applications.md
index 1bc43f4b7a4..7c24f6db86f 100644
--- a/doc/user/clusters/applications.md
+++ b/doc/user/clusters/applications.md
@@ -255,6 +255,7 @@ The applications below can be uninstalled.
 | GitLab Runner  | 12.2+         | Any running pipelines will be canceled. |
 | Ingress  | 12.1+         | The associated load balancer and IP will be deleted and cannot be restored. Furthermore, it can only be uninstalled if JupyterHub is not installed. |
 | JupyterHub  | 12.1+         | All data not committed to GitLab will be deleted and cannot be restored. |
+| Knative  | 12.1+         | The associated IP will be deleted and cannot be restored. |
 | Prometheus  | 11.11+         | All data will be deleted and cannot be restored. |
 
 To uninstall an application:
diff --git a/lib/gitlab/kubernetes/helm/delete_command.rb b/lib/gitlab/kubernetes/helm/delete_command.rb
index 876994d2678..aeba4a54b6d 100644
--- a/lib/gitlab/kubernetes/helm/delete_command.rb
+++ b/lib/gitlab/kubernetes/helm/delete_command.rb
@@ -7,19 +7,24 @@ module Gitlab
         include BaseCommand
         include ClientCommand
 
+        attr_reader :predelete, :postdelete
         attr_accessor :name, :files
 
-        def initialize(name:, rbac:, files:)
+        def initialize(name:, rbac:, files:, predelete: nil, postdelete: nil)
           @name = name
           @files = files
           @rbac = rbac
+          @predelete = predelete
+          @postdelete = postdelete
         end
 
         def generate_script
           super + [
             init_command,
             wait_for_tiller_command,
-            delete_command
+            predelete,
+            delete_command,
+            postdelete
           ].compact.join("\n")
         end
 
diff --git a/lib/gitlab/kubernetes/helm/install_command.rb b/lib/gitlab/kubernetes/helm/install_command.rb
index 9744a5f3d8a..f572bc43533 100644
--- a/lib/gitlab/kubernetes/helm/install_command.rb
+++ b/lib/gitlab/kubernetes/helm/install_command.rb
@@ -27,9 +27,9 @@ module Gitlab
             wait_for_tiller_command,
             repository_command,
             repository_update_command,
-            preinstall_command,
+            preinstall,
             install_command,
-            postinstall_command
+            postinstall
           ].compact.join("\n")
         end
 
@@ -58,14 +58,6 @@ module Gitlab
           command.shelljoin
         end
 
-        def preinstall_command
-          preinstall.join("\n") if preinstall
-        end
-
-        def postinstall_command
-          postinstall.join("\n") if postinstall
-        end
-
         def install_flag
           ['--install']
         end
diff --git a/locale/gitlab.pot b/locale/gitlab.pot
index 878ee5bc344..709226e686c 100644
--- a/locale/gitlab.pot
+++ b/locale/gitlab.pot
@@ -2815,7 +2815,7 @@ msgstr ""
 msgid "ClusterIntegration|The URL used to access the Kubernetes API."
 msgstr ""
 
-msgid "ClusterIntegration|The associated IP will be deleted and cannot be restored."
+msgid "ClusterIntegration|The associated IP and all deployed services will be deleted and cannot be restored. Uninstalling Knative will also remove Istio from your cluster. This will not effect any other applications."
 msgstr ""
 
 msgid "ClusterIntegration|The associated certifcate will be deleted and cannot be restored."
diff --git a/spec/features/projects/clusters/applications_spec.rb b/spec/features/projects/clusters/applications_spec.rb
index d0182270d82..de97c8a8bc0 100644
--- a/spec/features/projects/clusters/applications_spec.rb
+++ b/spec/features/projects/clusters/applications_spec.rb
@@ -126,7 +126,7 @@ describe 'Clusters Applications', :js do
             it 'shows status transition' do
               page.within('.js-cluster-application-row-knative') do
                 expect(domainname_form_value).to eq('domain.example.org')
-                expect(page).to have_css('.js-cluster-application-install-button', exact_text: 'Installed')
+                expect(page).to have_css('.js-cluster-application-uninstall-button', exact_text: 'Uninstall')
               end
 
               expect(page).to have_content('Knative was successfully installed on your Kubernetes cluster')
diff --git a/spec/models/clusters/applications/cert_manager_spec.rb b/spec/models/clusters/applications/cert_manager_spec.rb
index 8d853a04e33..6e1f80cadc2 100644
--- a/spec/models/clusters/applications/cert_manager_spec.rb
+++ b/spec/models/clusters/applications/cert_manager_spec.rb
@@ -48,7 +48,7 @@ describe Clusters::Applications::CertManager do
       expect(subject.version).to eq('v0.5.2')
       expect(subject).to be_rbac
       expect(subject.files).to eq(cert_manager.files.merge(cluster_issuer_file))
-      expect(subject.postinstall).to eq(['/usr/bin/kubectl create -f /data/helm/certmanager/config/cluster_issuer.yaml'])
+      expect(subject.postinstall).to eq(['kubectl create -f /data/helm/certmanager/config/cluster_issuer.yaml'])
     end
 
     context 'for a specific user' do
diff --git a/spec/models/clusters/applications/knative_spec.rb b/spec/models/clusters/applications/knative_spec.rb
index 7f4819cbb9a..342ed907854 100644
--- a/spec/models/clusters/applications/knative_spec.rb
+++ b/spec/models/clusters/applications/knative_spec.rb
@@ -39,7 +39,7 @@ describe Clusters::Applications::Knative do
   describe '#can_uninstall?' do
     subject { knative.can_uninstall? }
 
-    it { is_expected.to be_falsey }
+    it { is_expected.to be_truthy }
   end
 
   describe '#schedule_status_update with external_ip' do
@@ -129,6 +129,46 @@ describe Clusters::Applications::Knative do
     it_behaves_like 'a command'
   end
 
+  describe '#uninstall_command' do
+    subject { knative.uninstall_command }
+
+    it { is_expected.to be_an_instance_of(Gitlab::Kubernetes::Helm::DeleteCommand) }
+
+    it "removes knative deployed services before uninstallation" do
+      2.times do |i|
+        cluster_project = create(:cluster_project, cluster: knative.cluster)
+
+        create(:cluster_kubernetes_namespace,
+          cluster: cluster_project.cluster,
+          cluster_project: cluster_project,
+          project: cluster_project.project,
+          namespace: "namespace_#{i}")
+      end
+
+      remove_namespaced_services_script = [
+        "kubectl delete ksvc --all -n #{knative.cluster.kubernetes_namespaces.first.namespace}",
+        "kubectl delete ksvc --all -n #{knative.cluster.kubernetes_namespaces.second.namespace}"
+      ]
+
+      expect(subject.predelete).to match_array(remove_namespaced_services_script)
+    end
+
+    it "initializes command with all necessary postdelete script" do
+      api_resources = YAML.safe_load(File.read(Rails.root.join(Clusters::Applications::Knative::API_RESOURCES_PATH)))
+
+      remove_knative_istio_leftovers_script = [
+        "kubectl delete --ignore-not-found ns knative-serving",
+        "kubectl delete --ignore-not-found ns knative-build"
+      ]
+
+      full_delete_commands_size = api_resources.size + remove_knative_istio_leftovers_script.size
+
+      expect(subject.postdelete).to include(*remove_knative_istio_leftovers_script)
+      expect(subject.postdelete.size).to eq(full_delete_commands_size)
+      expect(subject.postdelete[2]).to eq("kubectl delete --ignore-not-found crd #{api_resources[0]}")
+    end
+  end
+
   describe '#files' do
     let(:application) { knative }
     let(:values) { subject[:'values.yaml'] }