If a cluster is blocked, it is not configured

This should fix the error in
https://gitlab.com/gitlab-org/gitlab/issues/202064 which is causing job
logs not to show.

app/models/clusters/applications/prometheus.rb

@@ -99,6 +99,8 @@ module Clusters
 
       def configured?
         kube_client.present? && available?
+      rescue Gitlab::UrlBlocker::BlockedUrlError
+        false
       end
 
       private

changelogs/unreleased/fix_prometheus_configured_blocked.yml

+---
+title: Fix job page not loading because kuberenetes/prometheus URL is blocked
+merge_request: 24743
+author:
+type: fixed

spec/models/clusters/applications/prometheus_spec.rb

@@ -4,6 +4,7 @@ require 'spec_helper'
 
 describe Clusters::Applications::Prometheus do
   include KubernetesHelpers
+  include StubRequests
 
   include_examples 'cluster application core specs', :clusters_applications_prometheus
   include_examples 'cluster application status specs', :clusters_applications_prometheus
@@ -320,6 +321,16 @@ describe Clusters::Applications::Prometheus do
 
         it { is_expected.to be_falsey }
       end
+
+      context 'when the kubernetes URL is blocked' do
+        before do
+          blocked_ip = '127.0.0.1' # localhost addresses are blocked by default
+
+          stub_all_dns(cluster.platform.api_url, ip_address: blocked_ip)
+        end
+
+        it { is_expected.to be_falsey }
+      end
     end
 
     context 'when a kubenetes client is not present' do