Generate serverless UUID and assign it by default

- Create a method to generate serverless UUIDs
- Assign a UUID to Serverless::DomainCluster by default

app/models/serverless/domain_cluster.rb

@@ -4,11 +4,16 @@ module Serverless
   class DomainCluster < ApplicationRecord
     self.table_name = 'serverless_domain_cluster'
 
+    HEX_REGEXP = %r{\A\h+\z}.freeze
+
     belongs_to :pages_domain
     belongs_to :knative, class_name: 'Clusters::Applications::Knative', foreign_key: 'clusters_applications_knative_id'
     belongs_to :creator, class_name: 'User', optional: true
 
-    validates :pages_domain, :knative, :uuid, presence: true
-    validates :uuid, uniqueness: true, length: { is: 14 }
+    validates :pages_domain, :knative, presence: true
+    validates :uuid, presence: true, uniqueness: true, length: { is: Gitlab::Serverless::Domain::UUID_LENGTH },
+              format: { with: HEX_REGEXP, message: 'only allows hex characters' }
+
+    default_value_for(:uuid, allows_nil: false) { Gitlab::Serverless::Domain.generate_uuid }
   end
 end

lib/gitlab/prometheus/queries/knative_invocation_query.rb

@@ -20,7 +20,7 @@ module Gitlab
         protected
 
         def context(function_id)
-          function = Serverless::Function.find_by_id(function_id)
+          function = ::Serverless::Function.find_by_id(function_id)
           {
             function_name: function.name,
             kube_namespace: function.namespace

lib/gitlab/serverless/domain.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Serverless
+    class Domain
+      UUID_LENGTH = 14
+
+      def self.generate_uuid
+        SecureRandom.hex(UUID_LENGTH / 2)
+      end
+    end
+  end
+end

spec/factories/serverless/domain_cluster.rb

@@ -5,6 +5,5 @@ FactoryBot.define do
     pages_domain { create(:pages_domain) }
     knative { create(:clusters_applications_knative) }
     creator { create(:user) }
-    uuid { SecureRandom.hex(7) }
   end
 end

spec/lib/gitlab/serverless/domain_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Serverless::Domain do
+  describe '.generate_uuid' do
+    it 'has 14 characters' do
+      expect(described_class.generate_uuid.length).to eq(described_class::UUID_LENGTH)
+    end
+
+    it 'consists of only hexadecimal characters' do
+      expect(described_class.generate_uuid).to match(/\A\h+\z/)
+    end
+
+    it 'uses random characters' do
+      uuid = 'abcd1234567890'
+
+      expect(SecureRandom).to receive(:hex).with(described_class::UUID_LENGTH / 2).and_return(uuid)
+      expect(described_class.generate_uuid).to eq(uuid)
+    end
+  end
+end

spec/models/serverless/domain_cluster_spec.rb

@@ -8,10 +8,17 @@ describe Serverless::DomainCluster do
   describe 'validations' do
     it { is_expected.to validate_presence_of(:pages_domain) }
     it { is_expected.to validate_presence_of(:knative) }
-    it { is_expected.to validate_presence_of(:uuid) }
 
+    it { is_expected.to validate_presence_of(:uuid) }
+    it { is_expected.to validate_length_of(:uuid).is_equal_to(Gitlab::Serverless::Domain::UUID_LENGTH) }
     it { is_expected.to validate_uniqueness_of(:uuid) }
-    it { is_expected.to validate_length_of(:uuid).is_equal_to(14) }
+
+    it 'validates that uuid has only hex characters' do
+      subject = build(:serverless_domain_cluster, uuid: 'z1234567890123')
+      subject.valid?
+
+      expect(subject.errors[:uuid]).to include('only allows hex characters')
+    end
   end
 
   describe 'associations' do
@@ -19,4 +26,24 @@ describe Serverless::DomainCluster do
     it { is_expected.to belong_to(:knative) }
     it { is_expected.to belong_to(:creator).optional }
   end
+
+  describe 'uuid' do
+    context 'when nil' do
+      it 'generates a value by default' do
+        attributes = build(:serverless_domain_cluster).attributes.merge(uuid: nil)
+        expect(Gitlab::Serverless::Domain).to receive(:generate_uuid).and_call_original
+
+        subject = Serverless::DomainCluster.new(attributes)
+
+        expect(subject.uuid).not_to be_blank
+      end
+    end
+
+    context 'when not nil' do
+      it 'does not override the existing value' do
+        uuid = 'abcd1234567890'
+        expect(build(:serverless_domain_cluster, uuid: uuid).uuid).to eq(uuid)
+      end
+    end
+  end
 end