Merge branch 'stomlinson/service-discovery-prefork' into 'master'

Run serivce discovery on load balancing configuration

See merge request gitlab-org/gitlab!68378

lib/gitlab/database/load_balancing.rb

@@ -108,6 +108,11 @@ module Gitlab
       # Configures proxying of requests.
       def self.configure_proxy(proxy = ConnectionProxy.new(hosts))
         ActiveRecord::Base.load_balancing_proxy = proxy
+
+        # Populate service discovery immediately if it is configured
+        if service_discovery_enabled?
+          ServiceDiscovery.new(service_discovery_configuration).perform_service_discovery
+        end
       end
 
       def self.active_record_models

lib/gitlab/database/load_balancing/service_discovery.rb

@@ -63,18 +63,14 @@ module Gitlab
         end
 
         def start
-          # We run service discovery once in the current thread so that the application's main thread
-          # does not race this thread to use the results of initial service discovery.
-          next_sleep_duration = perform_service_discovery
-
           Thread.new do
             loop do
+              next_sleep_duration = perform_service_discovery
+
               # We slightly randomize the sleep() interval. This should reduce
               # the likelihood of _all_ processes refreshing at the same time,
               # possibly putting unnecessary pressure on the DNS server.
               sleep(next_sleep_duration + rand(MAX_SLEEP_ADJUSTMENT))
-
-              next_sleep_duration = perform_service_discovery
             end
           end
         end

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

@@ -57,16 +57,13 @@ RSpec.describe Gitlab::Database::LoadBalancing::ServiceDiscovery do
         .and_yield
     end
 
-    it 'runs service discovery once before starting the worker thread' do
-      expect(service).to receive(:perform_service_discovery).ordered.and_return(5)
-
+    it 'starts service discovery in a new thread' do
       expect(Thread).to receive(:new).ordered.and_call_original # Thread starts
 
+      expect(service).to receive(:perform_service_discovery).ordered.and_return(5)
       expect(service).to receive(:rand).ordered.and_return(2)
       expect(service).to receive(:sleep).ordered.with(7) # Sleep runs after thread starts
 
-      expect(service).to receive(:perform_service_discovery).ordered.and_return(1)
-
       service.start.join
     end
   end

spec/lib/gitlab/database/load_balancing_spec.rb

@@ -212,6 +212,21 @@ RSpec.describe Gitlab::Database::LoadBalancing do
       expect(ActiveRecord::Base).to have_received(:load_balancing_proxy=)
         .with(Gitlab::Database::LoadBalancing::ConnectionProxy)
     end
+
+    context 'when service discovery is enabled' do
+      let(:service_discovery) { double(Gitlab::Database::LoadBalancing::ServiceDiscovery) }
+
+      it 'runs initial service discovery when configuring the connection proxy' do
+        allow(described_class)
+          .to receive(:configuration)
+          .and_return('discover' => { 'record' => 'foo' })
+
+        expect(Gitlab::Database::LoadBalancing::ServiceDiscovery).to receive(:new).and_return(service_discovery)
+        expect(service_discovery).to receive(:perform_service_discovery)
+
+        described_class.configure_proxy
+      end
+    end
   end
 
   describe '.active_record_models' do