Enfouce namespace for Kubernetes to lowercase

app/models/project_services/kubernetes_service.rb

@@ -24,6 +24,8 @@ class KubernetesService < DeploymentService
     validates :token
   end
 
+  before_validation :enforce_namespace_to_lower_case
+
   validates :namespace,
     allow_blank: true,
     length: 1..63,
@@ -207,4 +209,8 @@ class KubernetesService < DeploymentService
       max_session_time: current_application_settings.terminal_max_session_time
     }
   end
+
+  def enforce_namespace_to_lower_case
+    self.namespace = self.namespace&.downcase
+  end
 end

lib/gitlab/regex.rb

@@ -53,7 +53,8 @@ module Gitlab
     end
 
     def kubernetes_namespace_regex_message
-      "can contain only letters, digits or '-', and cannot start or end with '-'"
+      "can contain only lowercase letters, digits, and '-'. " \
+      "Must start with a letter, and cannot end with '-'"
     end
 
     def environment_slug_regex

spec/models/project_services/kubernetes_service_spec.rb

@@ -38,7 +38,8 @@ describe KubernetesService, :use_clean_rails_memory_store_caching do
           'a' * 63 => true,
           'a' * 64 => false,
           'a.b' => false,
-          'a*b' => false
+          'a*b' => false,
+          'FOO' => true,
         }.each do |namespace, validity|
           it "validates #{namespace} as #{validity ? 'valid' : 'invalid'}" do
             subject.namespace = namespace