Validate against mixing of group and project clusters

If project type clusters, it should only have projects assigned.
Similarly with groups.

app/models/clusters/cluster.rb

@@ -40,6 +40,9 @@ module Clusters
     validates :name, cluster_name: true
     validate :restrict_modification, on: :update
+    validate :no_groups, unless: :group_type?
+    validate :no_projects, unless: :project_type?
+
     delegate :status, to: :provider, allow_nil: true
     delegate :status_reason, to: :provider, allow_nil: true
     delegate :on_creation?, to: :provider, allow_nil: true
@@ -50,6 +53,12 @@ module Clusters
     delegate :available?, to: :application_ingress, prefix: true, allow_nil: true
     delegate :available?, to: :application_prometheus, prefix: true, allow_nil: true
+    enum cluster_type: {
+      instance_type: 1,
+      group_type: 2,
+      project_type: 3
+    }
+
     enum platform_type: {
       kubernetes: 1
     }
@@ -129,5 +138,17 @@ module Clusters
       true
     end
+
+    def no_groups
+      if groups.any?
+        errors.add(:cluster, 'cannot have groups assigned')
+      end
+    end
+
+    def no_projects
+      if projects.any?
+        errors.add(:cluster, 'cannot have projects assigned')
+      end
+    end
   end
 end

app/models/concerns/deployment_platform.rb

@@ -42,6 +42,7 @@ module DeploymentPlatform
     {
       name: 'kubernetes-template',
       projects: [self],
+      cluster_type: :project_type,
       provider_type: :user,
       platform_type: :kubernetes,
       platform_kubernetes_attributes: platform_kubernetes_attributes_from_service_template

app/services/clusters/create_service.rb

@@ -16,9 +16,9 @@ module Clusters
       end
       if project
-        cluster_params = params.merge(user: current_user, projects: [project])
+        cluster_params = params.merge(user: current_user, cluster_type: :project_type, projects: [project])
       elsif group
-        cluster_params = params.merge(user: current_user, groups: [group])
+        cluster_params = params.merge(user: current_user, cluster_type: :group_type, groups: [group])
       end
       cluster_params[:provider_gcp_attributes].try do |provider|

db/migrate/20181017001059_add_cluster_type_to_clusters.rb

+# frozen_string_literal: true
+
+class AddClusterTypeToClusters < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    add_column :clusters, :cluster_type, :smallint
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
-ActiveRecord::Schema.define(version: 20181014203236) do
+ActiveRecord::Schema.define(version: 20181017001059) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -637,6 +637,7 @@ ActiveRecord::Schema.define(version: 20181014203236) do
     t.boolean "enabled", default: true
     t.string "name", null: false
     t.string "environment_scope", default: "*", null: false
+    t.integer "cluster_type", limit: 2
   end
   add_index "clusters", ["enabled"], name: "index_clusters_on_enabled", using: :btree

spec/factories/clusters/clusters.rb

@@ -2,14 +2,23 @@ FactoryBot.define do
   factory :cluster, class: Clusters::Cluster do
     user
     name 'test-cluster'
+    cluster_type :project_type
+
+    trait :instance do
+      cluster_type :instance_type
+    end
     trait :project do
+      cluster_type :project_type
+
       before(:create) do |cluster, evaluator|
         cluster.projects << create(:project, :repository)
       end
     end
     trait :group do
+      cluster_type :group_type
+
       before(:create) do |cluster, evalutor|
         cluster.groups << create(:group)
       end

spec/models/clusters/cluster_spec.rb

@@ -177,6 +177,46 @@ describe Clusters::Cluster do
         it { expect(cluster.update(enabled: false)).to be_truthy }
       end
     end
+
+    describe 'cluster_type validations' do
+      let(:instance_cluster) { create(:cluster, :instance) }
+      let(:group_cluster) { create(:cluster, :group) }
+      let(:project_cluster) { create(:cluster, :project) }
+
+      context 'project_type cluster' do
+        it 'does not allow setting group' do
+          project_cluster.groups << build(:group)
+
+          expect(project_cluster).not_to be_valid
+          expect(project_cluster.errors.full_messages).to include('Cluster cannot have groups assigned')
+        end
+      end
+
+      context 'group_type cluster' do
+        it 'does not allow setting project' do
+          group_cluster.projects << build(:project)
+
+          expect(group_cluster).not_to be_valid
+          expect(group_cluster.errors.full_messages).to include('Cluster cannot have projects assigned')
+        end
+      end
+
+      context 'instance_type cluster' do
+        it 'does not allow setting group' do
+          instance_cluster.groups << build(:group)
+
+          expect(instance_cluster).not_to be_valid
+          expect(instance_cluster.errors.full_messages).to include('Cluster cannot have groups assigned')
+        end
+
+        it 'does not allow setting project' do
+          instance_cluster.projects << build(:project)
+
+          expect(instance_cluster).not_to be_valid
+          expect(instance_cluster.errors.full_messages).to include('Cluster cannot have projects assigned')
+        end
+      end
+    end
   end
   describe '#provider' do