Create one Kubernetes namespace for a deployment

Instead of creating a Kubernetes namespace on every
cluster related to a project, only create one on the
cluster the project is about to be deployed to.

app/models/deployment.rb

@@ -78,6 +78,10 @@ class Deployment < ActiveRecord::Base
     Commit.truncate_sha(sha)
   end
 
+  def cluster
+    project.deployment_platform(environment: environment.name)&.cluster
+  end
+
   def last?
     self == environment.last_deployment
   end

lib/gitlab/ci/build/prerequisite/base.rb

@@ -5,8 +5,6 @@ module Gitlab
     module Build
       module Prerequisite
         class Base
-          include Utils::StrongMemoize
-
           attr_reader :build
 
           def initialize(build)

lib/gitlab/ci/build/prerequisite/kubernetes_namespace.rb

@@ -10,37 +10,29 @@ module Gitlab
           # so we must always ensure the namespace is up to date.
           #
           def unmet?
-            build.has_deployment? && clusters_missing_namespaces.present?
+            deployment_cluster.present?
           end
 
           def complete!
             return unless unmet?
 
-            clusters_missing_namespaces.each do |cluster|
-              create_or_update_namespace(cluster)
-            end
+            create_or_update_namespace
           end
 
           private
 
-          def project
-            build.project
+          def deployment_cluster
+            build.deployment&.cluster
           end
 
-          def create_or_update_namespace(cluster)
-            kubernetes_namespace = cluster.find_or_initialize_kubernetes_namespace_for_project(project)
+          def create_or_update_namespace
+            kubernetes_namespace = deployment_cluster.find_or_initialize_kubernetes_namespace_for_project(build.project)
 
             Clusters::Gcp::Kubernetes::CreateOrUpdateNamespaceService.new(
-              cluster: cluster,
+              cluster: deployment_cluster,
               kubernetes_namespace: kubernetes_namespace
             ).execute
           end
-
-          def clusters_missing_namespaces
-            strong_memoize(:clusters_missing_namespaces) do
-              project.all_clusters.missing_kubernetes_namespace(project.kubernetes_namespaces).to_a
-            end
-          end
         end
       end
     end

spec/lib/gitlab/ci/build/prerequisite/kubernetes_namespace_spec.rb

@@ -16,34 +16,41 @@ describe Gitlab::Ci::Build::Prerequisite::KubernetesNamespace do
       it { is_expected.to be_falsey }
     end
 
-    context 'build has a deployment, and no existing kubernetes namespace' do
+    context 'build has a deployment' do
       let!(:deployment) { create(:deployment, deployable: build) }
-      let!(:cluster) { create(:cluster, projects: [build.project]) }
+
+      context 'and a cluster to deploy to' do
+        let(:cluster) { create(:cluster, projects: [build.project]) }
 
         before do
-        expect(build.project.kubernetes_namespaces).to be_empty
+          allow(build.deployment).to receive(:cluster).and_return(cluster)
         end
 
         it { is_expected.to be_truthy }
       end
 
-    context 'build has a deployment and kubernetes namespaces' do
-      let!(:deployment) { create(:deployment, deployable: build) }
-      let!(:cluster) { create(:cluster, projects: [build.project]) }
-      let!(:kubernetes_namespace) { create(:cluster_kubernetes_namespace, cluster: cluster) }
+      context 'and no cluster to deploy to' do
+        before do
+          expect(deployment.cluster).to be_nil
+        end
 
         it { is_expected.to be_falsey }
       end
     end
+  end
 
   describe '#complete!' do
-    let(:cluster) { create(:cluster, projects: [build.project]) }
+    let!(:deployment) { create(:deployment, deployable: build) }
     let(:service) { double(execute: true) }
 
     subject { described_class.new(build).complete! }
 
     context 'completion is required' do
-      let!(:deployment) { create(:deployment, deployable: build) }
+      let(:cluster) { create(:cluster, projects: [build.project]) }
+
+      before do
+        allow(build.deployment).to receive(:cluster).and_return(cluster)
+      end
 
       it 'creates a kubernetes namespace' do
         expect(Clusters::Gcp::Kubernetes::CreateOrUpdateNamespaceService)
@@ -59,7 +66,7 @@ describe Gitlab::Ci::Build::Prerequisite::KubernetesNamespace do
 
     context 'completion is not required' do
       before do
-        expect(build.deployment).to be_nil
+        expect(deployment.cluster).to be_nil
       end
 
       it 'does not create a namespace' do

spec/models/deployment_spec.rb

@@ -356,4 +356,32 @@ describe Deployment do
       end
     end
   end
+
+  describe '#cluster' do
+    let(:deployment) { create(:deployment) }
+    let(:project) { deployment.project }
+    let(:environment) { deployment.environment }
+
+    subject { deployment.cluster }
+
+    before do
+      expect(project).to receive(:deployment_platform)
+        .with(environment: environment.name).and_call_original
+    end
+
+    context 'project has no deployment platform' do
+      before do
+        expect(project.clusters).to be_empty
+      end
+
+      it { is_expected.to be_nil }
+    end
+
+    context 'project has a deployment platform' do
+      let!(:cluster) { create(:cluster, projects: [project]) }
+      let!(:platform) { create(:cluster_platform_kubernetes, cluster: cluster) }
+
+      it { is_expected.to eq cluster }
+    end
+  end
 end