Do not run service discovery for DB load balancing for rake tasks

Changelog: fixed

lib/gitlab/database/load_balancing/configuration.rb

@@ -107,7 +107,11 @@ module Gitlab
           hosts.any? || service_discovery_enabled?
         end
 
+        # This is disabled for Rake tasks to ensure e.g. database migrations
+        # always produce consistent results.
         def service_discovery_enabled?
+          return false if Gitlab::Runtime.rake?
+
           service_discovery[:record].present?
         end
 

spec/lib/gitlab/database/load_balancing/configuration_spec.rb

@@ -140,6 +140,15 @@ RSpec.describe Gitlab::Database::LoadBalancing::Configuration do
   end
 
   describe '#service_discovery_enabled?' do
+    it 'returns false when running inside a Rake task' do
+      allow(Gitlab::Runtime).to receive(:rake?).and_return(true)
+
+      config = described_class.new(ActiveRecord::Base)
+      config.service_discovery[:record] = 'foo'
+
+      expect(config.service_discovery_enabled?).to eq(false)
+    end
+
     it 'returns true when a record is configured' do
       config = described_class.new(ActiveRecord::Base)
       config.service_discovery[:record] = 'foo'

spec/lib/gitlab/database/load_balancing/service_discovery_spec.rb

@@ -4,9 +4,10 @@ require 'spec_helper'
 
 RSpec.describe Gitlab::Database::LoadBalancing::ServiceDiscovery do
   let(:load_balancer) do
-    Gitlab::Database::LoadBalancing::LoadBalancer.new(
-      Gitlab::Database::LoadBalancing::Configuration.new(ActiveRecord::Base)
-    )
+    configuration = Gitlab::Database::LoadBalancing::Configuration.new(ActiveRecord::Base)
+    configuration.service_discovery[:record] = 'localhost'
+
+    Gitlab::Database::LoadBalancing::LoadBalancer.new(configuration)
   end
 
   let(:service) do
@@ -86,6 +87,7 @@ RSpec.describe Gitlab::Database::LoadBalancing::ServiceDiscovery do
         service.perform_service_discovery
       end
     end
+
     context 'with failures' do
       before do
         allow(Gitlab::ErrorTracking).to receive(:track_exception)