Generate KUBECONFIG in KubernetesService#predefined_variables

app/models/project_services/kubernetes_service.rb

@@ -96,10 +96,14 @@ class KubernetesService < DeploymentService
   end
 
   def predefined_variables
+    config = YAML.dump(kubeconfig)
+
     variables = [
       { key: 'KUBE_URL', value: api_url, public: true },
       { key: 'KUBE_TOKEN', value: token, public: false },
-      { key: 'KUBE_NAMESPACE', value: actual_namespace, public: true }
+      { key: 'KUBE_NAMESPACE', value: actual_namespace, public: true },
+      { key: 'KUBECONFIG', value: config, public: false },
+      { key: 'KUBECONFIG_FILE', value: config, public: false, file: true },
     ]
 
     if ca_pem.present?
@@ -135,6 +139,14 @@ class KubernetesService < DeploymentService
 
   private
 
+  def kubeconfig
+    to_kubeconfig(
+      url: api_url,
+      namespace: actual_namespace,
+      token: token,
+      ca_pem: ca_pem)
+  end
+
   def namespace_placeholder
     default_namespace || TEMPLATE_PLACEHOLDER
   end

lib/gitlab/kubernetes.rb

@@ -76,5 +76,44 @@ module Gitlab
 
       url.to_s
     end
+
+    def to_kubeconfig(url:, namespace:, token:, ca_pem: nil)
+      config = {
+        apiVersion: 'v1',
+        clusters: [
+          name: 'gitlab-deploy',
+          cluster: {
+            server: url
+          },
+        ],
+        contexts: [
+          name: 'gitlab-deploy',
+          context: {
+            cluster: 'gitlab-deploy',
+            namespace: namespace,
+            user: 'gitlab-deploy'
+          },
+        ],
+        :'current-context' => 'gitlab-deploy',
+        kind: 'Config',
+        users: [
+          {
+            name: 'gitlab-deploy',
+            user: {token: token}
+          }
+        ]
+      }
+
+      kubeconfig_embed_ca_pem(config, ca_pem) if ca_pem
+
+      config.deep_stringify_keys
+    end
+
+    private
+
+    def kubeconfig_embed_ca_pem(config, ca_pem)
+      cluster = config.dig(:clusters, 0, :cluster)
+      cluster[:'certificate-authority-data'] = ca_pem
+    end
   end
 end

spec/fixtures/config/kubeconfig-without-ca.yml

+---
+apiVersion: v1
+clusters:
+- name: gitlab-deploy
+  cluster:
+    server: https://kube.domain.com
+contexts:
+- name: gitlab-deploy
+  context:
+    cluster: gitlab-deploy
+    namespace: NAMESPACE
+    user: gitlab-deploy
+current-context: gitlab-deploy
+kind: Config
+users:
+- name: gitlab-deploy
+  user:
+    token: TOKEN

spec/fixtures/config/kubeconfig.yml

+---
+apiVersion: v1
+clusters:
+- name: gitlab-deploy
+  cluster:
+    server: https://kube.domain.com
+    certificate-authority-data: PEM
+contexts:
+- name: gitlab-deploy
+  context:
+    cluster: gitlab-deploy
+    namespace: NAMESPACE
+    user: gitlab-deploy
+current-context: gitlab-deploy
+kind: Config
+users:
+- name: gitlab-deploy
+  user:
+    token: TOKEN

spec/lib/gitlab/kubernetes_spec.rb

@@ -46,4 +46,28 @@ describe Gitlab::Kubernetes do
       expect(filter_by_label(items, app: 'foo')).to eq(matching_items)
     end
   end
+
+  describe '#to_kubeconfig' do
+    subject do
+      to_kubeconfig(
+        url: 'https://kube.domain.com',
+        namespace: 'NAMESPACE',
+        token: 'TOKEN',
+        ca_pem: ca_pem)
+    end
+
+    context 'when CA PEM is provided' do
+      let(:ca_pem) { 'PEM' }
+      let(:path) { expand_fixture_path('config/kubeconfig.yml') }
+
+      it { is_expected.to eq(YAML.load_file(path)) }
+    end
+
+    context 'when CA PEM is not provided' do
+      let(:ca_pem) { nil }
+      let(:path) { expand_fixture_path('config/kubeconfig-without-ca.yml') }
+
+      it { is_expected.to eq(YAML.load_file(path)) }
+    end
+  end
 end

spec/models/project_services/kubernetes_service_spec.rb

@@ -201,6 +201,13 @@ describe KubernetesService, models: true, caching: true do
   end
 
   describe '#predefined_variables' do
+    let(:kubeconfig) do
+      File.read(expand_fixture_path('config/kubeconfig.yml'))
+        .gsub('TOKEN', 'token')
+        .gsub('PEM', 'CA PEM DATA')
+        .gsub('NAMESPACE', namespace)
+    end
+
     before do
       subject.api_url = 'https://kube.domain.com'
       subject.token = 'token'
@@ -208,32 +215,35 @@ describe KubernetesService, models: true, caching: true do
       subject.project = project
     end
 
-    context 'namespace is provided' do
-      before do
-        subject.namespace = 'my-project'
-      end
-
+    shared_examples 'setting variables' do
       it 'sets the variables' do
         expect(subject.predefined_variables).to include(
           { key: 'KUBE_URL', value: 'https://kube.domain.com', public: true },
           { key: 'KUBE_TOKEN', value: 'token', public: false },
-          { key: 'KUBE_NAMESPACE', value: 'my-project', public: true },
+          { key: 'KUBE_NAMESPACE', value: namespace, public: true },
+          { key: 'KUBECONFIG', value: kubeconfig, public: false },
+          { key: 'KUBECONFIG_FILE', value: kubeconfig, public: false, file: true },
           { key: 'KUBE_CA_PEM', value: 'CA PEM DATA', public: true },
           { key: 'KUBE_CA_PEM_FILE', value: 'CA PEM DATA', public: true, file: true }
         )
       end
     end
 
-    context 'no namespace provided' do
-      it 'sets the variables' do
-        expect(subject.predefined_variables).to include(
-          { key: 'KUBE_URL', value: 'https://kube.domain.com', public: true },
-          { key: 'KUBE_TOKEN', value: 'token', public: false },
-          { key: 'KUBE_CA_PEM', value: 'CA PEM DATA', public: true },
-          { key: 'KUBE_CA_PEM_FILE', value: 'CA PEM DATA', public: true, file: true }
-        )
+    context 'namespace is provided' do
+      let(:namespace) { 'my-project' }
+
+      before do
+        subject.namespace = namespace
       end
 
+      it_behaves_like 'setting variables'
+    end
+
+    context 'no namespace provided' do
+      let(:namespace) { subject.actual_namespace }
+
+      it_behaves_like 'setting variables'
+
       it 'sets the KUBE_NAMESPACE' do
         kube_namespace = subject.predefined_variables.find { |h| h[:key] == 'KUBE_NAMESPACE' }