Remove TLD validation from Cluster#domain

app/models/clusters/cluster.rb

@@ -50,7 +50,7 @@ module Clusters
 
     validates :name, cluster_name: true
     validates :cluster_type, presence: true
-    validates :domain, allow_blank: true, hostname: { allow_numeric_hostname: true, require_valid_tld: true }
+    validates :domain, allow_blank: true, hostname: { allow_numeric_hostname: true }
 
     validate :restrict_modification, on: :update
     validate :no_groups, unless: :group_type?

changelogs/unreleased/57650-remove-tld-validation-from-cluster.yml

@@ -0,0 +1,5 @@
+---
+title: Fixes incorrect TLD validation errors for Kubernetes cluster domain
+merge_request: 25262
+author:
+type: fixed

spec/controllers/groups/clusters_controller_spec.rb

@@ -453,7 +453,7 @@ describe Groups::ClustersController do
     end
 
     context 'when domain is invalid' do
-      let(:domain) { 'not-a-valid-domain' }
+      let(:domain) { 'http://not-a-valid-domain' }
 
       it 'should not update cluster attributes' do
         go

spec/models/clusters/cluster_spec.rb

@@ -265,12 +265,12 @@ describe Clusters::Cluster do
         it { is_expected.to be_valid }
       end
 
-      context 'when cluster has an invalid domain' do
-        let(:cluster) { build(:cluster, domain: 'not-valid-domain') }
+      context 'when cluster is not a valid hostname' do
+        let(:cluster) { build(:cluster, domain: 'http://not.a.valid.hostname') }
 
         it 'should add an error on domain' do
           expect(subject).not_to be_valid
-          expect(subject.errors[:domain].first).to eq('is not a fully qualified domain name')
+          expect(subject.errors[:domain].first).to eq('contains invalid characters (valid characters: [a-z0-9\\-])')
         end
       end