Allow CI specified k8s namespace for deploy boards, terminals & pod logs

https://gitlab.com/gitlab-org/gitlab/merge_requests/21460

app/models/clusters/cluster.rb

@@ -249,14 +249,9 @@ module Clusters
     end
 
     def kubernetes_namespace_for(environment)
-      project = environment.project
-      persisted_namespace = Clusters::KubernetesNamespaceFinder.new(
-        self,
-        project: project,
-        environment_name: environment.name
-      ).execute
-
-      persisted_namespace&.namespace || Gitlab::Kubernetes::DefaultNamespace.new(self, project: project).from_environment_slug(environment.slug)
+      managed_namespace(environment) ||
+        ci_configured_namespace(environment) ||
+        default_namespace(environment)
     end
 
     def allow_user_defined_namespace?
@@ -308,6 +303,25 @@ module Clusters
       end
     end
 
+    def managed_namespace(environment)
+      Clusters::KubernetesNamespaceFinder.new(
+        self,
+        project: environment.project,
+        environment_name: environment.name
+      ).execute&.namespace
+    end
+
+    def ci_configured_namespace(environment)
+      environment.last_deployable&.expanded_kubernetes_namespace
+    end
+
+    def default_namespace(environment)
+      Gitlab::Kubernetes::DefaultNamespace.new(
+        self,
+        project: environment.project
+      ).from_environment_slug(environment.slug)
+    end
+
     def instance_domain
       @instance_domain ||= Gitlab::CurrentSettings.auto_devops_domain
     end

changelogs/unreleased/27630-use-ci-specified-namespace-for-deploy-boards.yml

+---
+title: Allow Kubernetes namespaces specified via CI template to be used for terminals,
+  pod logs and deploy boards
+merge_request: 21460
+author:
+type: added

spec/models/clusters/cluster_spec.rb

@@ -674,7 +674,8 @@ describe Clusters::Cluster, :use_clean_rails_memory_store_caching do
 
   describe '#kubernetes_namespace_for' do
     let(:cluster) { create(:cluster, :group) }
-    let(:environment) { create(:environment) }
+    let(:environment) { create(:environment, last_deployable: build) }
+    let(:build) { create(:ci_build) }
 
     subject { cluster.kubernetes_namespace_for(environment) }
 
@@ -682,16 +683,15 @@ describe Clusters::Cluster, :use_clean_rails_memory_store_caching do
       expect(Clusters::KubernetesNamespaceFinder).to receive(:new)
         .with(cluster, project: environment.project, environment_name: environment.name)
         .and_return(double(execute: persisted_namespace))
-    end
-
-    context 'a persisted namespace exists' do
-      let(:persisted_namespace) { create(:cluster_kubernetes_namespace) }
 
-      it { is_expected.to eq persisted_namespace.namespace }
+      allow(build).to receive(:expanded_kubernetes_namespace)
+        .and_return(ci_configured_namespace)
     end
 
-    context 'no persisted namespace exists' do
+    context 'no persisted namespace exists and namespace is not specified in CI template' do
       let(:persisted_namespace) { nil }
+      let(:ci_configured_namespace) { nil }
+
       let(:namespace_generator) { double }
       let(:default_namespace) { 'a-default-namespace' }
 
@@ -706,6 +706,27 @@ describe Clusters::Cluster, :use_clean_rails_memory_store_caching do
 
       it { is_expected.to eq default_namespace }
     end
+
+    context 'persisted namespace exists' do
+      let(:persisted_namespace) { create(:cluster_kubernetes_namespace) }
+      let(:ci_configured_namespace) { nil }
+
+      it { is_expected.to eq persisted_namespace.namespace }
+    end
+
+    context 'namespace is specified in CI template' do
+      let(:persisted_namespace) { nil }
+      let(:ci_configured_namespace) { 'ci-configured-namespace' }
+
+      it { is_expected.to eq ci_configured_namespace }
+    end
+
+    context 'persisted namespace exists and namespace is also specifed in CI template' do
+      let(:persisted_namespace) { create(:cluster_kubernetes_namespace) }
+      let(:ci_configured_namespace) { 'ci-configured-namespace' }
+
+      it { is_expected.to eq persisted_namespace.namespace }
+    end
   end
 
   describe '#predefined_variables' do