Add RoleBinding methods

Includes RoleBinding methods to Kubeclient and introduce a new lib class
to generate RoleBinding resources.

This MR is part of
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22011

changelogs/unreleased/add-role-binding-to-kubeclient.yml

+---
+title: Allow kubeclient to call RoleBinding methods
+merge_request: 22524
+author:
+type: other

lib/gitlab/kubernetes/kube_client.rb

@@ -45,6 +45,13 @@ module Gitlab
         :update_cluster_role_binding,
         to: :rbac_client
 
+      # RBAC methods delegates to the apis/rbac.authorization.k8s.io api
+      # group client
+      delegate :create_role_binding,
+        :get_role_binding,
+        :update_role_binding,
+        to: :rbac_client
+
       # Deployments resource is currently on the apis/extensions api group
       delegate :get_deployments,
         to: :extensions_client

lib/gitlab/kubernetes/role_binding.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Kubernetes
+    class RoleBinding
+      attr_reader :role_name, :namespace, :service_account_name
+
+      def initialize(role_name:, namespace:, service_account_name:)
+        @role_name = role_name
+        @namespace = namespace
+        @service_account_name = service_account_name
+      end
+
+      def generate
+        ::Kubeclient::Resource.new.tap do |resource|
+          resource.metadata = metadata
+          resource.roleRef  = role_ref
+          resource.subjects = subjects
+        end
+      end
+
+      private
+
+      def metadata
+        { name: "gitlab-#{namespace}", namespace: namespace }
+      end
+
+      def role_ref
+        {
+          apiGroup: 'rbac.authorization.k8s.io',
+          kind: 'Role',
+          name: role_name
+        }
+      end
+
+      def subjects
+        [
+          {
+            kind: 'ServiceAccount',
+            name: service_account_name,
+            namespace: namespace
+          }
+        ]
+      end
+    end
+  end
+end

spec/lib/gitlab/kubernetes/role_binding_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Kubernetes::RoleBinding, '#generate' do
+  let(:role_name) { 'edit' }
+  let(:namespace) { 'my-namespace' }
+  let(:service_account_name) { 'my-service-account' }
+
+  let(:subjects) do
+    [
+      {
+        kind: 'ServiceAccount',
+        name: service_account_name,
+        namespace: namespace
+      }
+    ]
+  end
+
+  let(:role_ref) do
+    {
+      apiGroup: 'rbac.authorization.k8s.io',
+      kind: 'Role',
+      name: role_name
+    }
+  end
+
+  let(:resource) do
+    ::Kubeclient::Resource.new(
+      metadata: { name: "gitlab-#{namespace}", namespace: namespace },
+      roleRef: role_ref,
+      subjects: subjects
+    )
+  end
+
+  subject do
+    described_class.new(
+      role_name: role_name,
+      namespace: namespace,
+      service_account_name: service_account_name
+    ).generate
+  end
+
+  it 'should build a Kubeclient Resource' do
+    is_expected.to eq(resource)
+  end
+end