Enable GitLabb runner to be uninstalled from cluster

- Set as uninstallable app
- Update docs
- Adjust specs

app/models/clusters/applications/runner.rb

@@ -29,13 +29,6 @@ module Clusters
         content_values.to_yaml
       end
 
-      # Need to investigate if pipelines run by this runner will stop upon the
-      # executor pod stopping
-      # I.e.run a pipeline, and uninstall runner while pipeline is running
-      def allowed_to_uninstall?
-        false
-      end
-
       def install_command
         Gitlab::Kubernetes::Helm::InstallCommand.new(
           name: name,
@@ -47,6 +40,14 @@ module Clusters
         )
       end
 
+      def prepare_uninstall
+        runner&.update!(active: false)
+      end
+
+      def post_uninstall
+        runner.destroy!
+      end
+
       private
 
       def ensure_runner

app/models/clusters/concerns/application_core.rb

@@ -46,6 +46,16 @@ module Clusters
             command.version = version
           end
         end
+
+        def prepare_uninstall
+          # Override if your application needs any action before
+          # being uninstalled by Helm
+        end
+
+        def post_uninstall
+          # Override if your application needs any action after
+          # being uninstalled by Helm
+        end
       end
     end
   end

app/models/clusters/concerns/application_status.rb

@@ -59,29 +59,33 @@ module Clusters
             transition [:scheduled] => :uninstalling
           end
 
-          before_transition any => [:scheduled] do |app_status, _|
-            app_status.status_reason = nil
+          before_transition any => [:scheduled] do |application, _|
+            application.status_reason = nil
           end
 
-          before_transition any => [:errored] do |app_status, transition|
+          before_transition any => [:errored] do |application, transition|
             status_reason = transition.args.first
-            app_status.status_reason = status_reason if status_reason
+            application.status_reason = status_reason if status_reason
           end
 
-          before_transition any => [:updating] do |app_status, _|
-            app_status.status_reason = nil
+          before_transition any => [:updating] do |application, _|
+            application.status_reason = nil
           end
 
-          before_transition any => [:update_errored, :uninstall_errored] do |app_status, transition|
+          before_transition any => [:update_errored, :uninstall_errored] do |application, transition|
             status_reason = transition.args.first
-            app_status.status_reason = status_reason if status_reason
+            application.status_reason = status_reason if status_reason
           end
 
-          before_transition any => [:installed, :updated] do |app_status, _|
+          before_transition any => [:installed, :updated] do |application, _|
             # When installing any application we are also performing an update
             # of tiller (see Gitlab::Kubernetes::Helm::ClientCommand) so
             # therefore we need to reflect that in the database.
-            app_status.cluster.application_helm.update!(version: Gitlab::Kubernetes::Helm::HELM_VERSION)
+            application.cluster.application_helm.update!(version: Gitlab::Kubernetes::Helm::HELM_VERSION)
+          end
+
+          after_transition any => [:uninstalling], :use_transactions => false do |application, _|
+            application.prepare_uninstall
           end
         end
       end

app/services/clusters/applications/check_uninstall_progress_service.rb

@@ -23,6 +23,7 @@ module Clusters
       private
 
       def on_success
+        app.post_uninstall
         app.destroy!
       rescue StandardError => e
         app.make_errored!(_('Application uninstalled but failed to destroy: %{error_message}') % { error_message: e.message })

changelogs/unreleased/60666-kubernetes-applications-uninstall-runner.yml

@@ -0,0 +1,5 @@
+---
+title: Allow GitLab Runner to be uninstalled from the UI
+merge_request: 30176
+author:
+type: added

doc/user/clusters/applications.md

@@ -251,6 +251,7 @@ The applications below can be uninstalled.
 
 | Application | GitLab version | Notes |
 | ----------- | -------------- | ----- |
+| 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. |
 | Prometheus  | 11.11+         | All data will be deleted and cannot be restored. |
@@ -278,7 +279,7 @@ Error: remote error: tls: bad certificate
 To avoid installation errors:
 
 - Before starting the installation of applications, make sure that time is synchronized
-  between your GitLab server and your Kubernetes cluster.
+between your GitLab server and your Kubernetes cluster.
 - Ensure certificates are not out of sync. When installing applications, GitLab expects a new cluster with no previous installation of Helm.
 
   You can confirm that the certificates match via `kubectl`:

spec/models/clusters/applications/runner_spec.rb

@@ -18,7 +18,7 @@ describe Clusters::Applications::Runner do
 
     subject { gitlab_runner.can_uninstall? }
 
-    it { is_expected.to be_falsey }
+    it { is_expected.to be_truthy }
   end
 
   describe '#install_command' do
@@ -156,4 +156,35 @@ describe Clusters::Applications::Runner do
       end
     end
   end
+
+  describe '#prepare_uninstall' do
+    it 'pauses associated runner' do
+      active_runner = create(:ci_runner, contacted_at: 1.second.ago)
+
+      expect(active_runner.status).to eq(:online)
+
+      application_runner = create(:clusters_applications_runner, :scheduled, runner: active_runner)
+      application_runner.prepare_uninstall
+
+      expect(active_runner.status).to eq(:paused)
+    end
+  end
+
+  describe '#make_uninstalling!' do
+    subject { create(:clusters_applications_runner, :scheduled, runner: ci_runner) }
+
+    it 'calls prepare_uninstall' do
+      expect_any_instance_of(described_class).to receive(:prepare_uninstall).and_call_original
+
+      subject.make_uninstalling!
+    end
+  end
+
+  describe '#post_uninstall' do
+    it 'destroys its runner' do
+      application_runner = create(:clusters_applications_runner, :scheduled, runner: ci_runner)
+
+      expect { application_runner.post_uninstall }.to change { Ci::Runner.count }.by(-1)
+    end
+  end
 end

spec/services/clusters/applications/check_uninstall_progress_service_spec.rb

@@ -41,7 +41,7 @@ describe Clusters::Applications::CheckUninstallProgressService do
     end
   end
 
-  context 'when application is installing' do
+  context 'when application is uninstalling' do
     RESCHEDULE_PHASES.each { |phase| it_behaves_like 'a not yet terminated installation', phase }
 
     context 'when installation POD succeeded' do
@@ -56,6 +56,12 @@ describe Clusters::Applications::CheckUninstallProgressService do
         service.execute
       end
 
+      it 'runs application post_uninstall' do
+        expect(application).to receive(:post_uninstall).and_call_original
+
+        service.execute
+      end
+
       it 'destroys the application' do
         expect(worker_class).not_to receive(:perform_in)