Log every service discovery event

lib/gitlab/database/load_balancing/host_list.rb

@@ -35,12 +35,6 @@ module Gitlab
 
         def hosts=(hosts)
           @mutex.synchronize do
-            ::Gitlab::Database::LoadBalancing::Logger.info(
-              event: :host_list_update,
-              message: "Updating the host list for service discovery",
-              host_list_length: hosts.length,
-              old_host_list_length: @hosts.length
-            )
             @hosts = hosts
             unsafe_shuffle
           end

lib/gitlab/database/load_balancing/service_discovery.rb

@@ -99,7 +99,22 @@ module Gitlab
 
           current = addresses_from_load_balancer
 
-          replace_hosts(from_dns) if from_dns != current
+          if from_dns != current
+            ::Gitlab::Database::LoadBalancing::Logger.info(
+              event: :host_list_update,
+              message: "Updating the host list for service discovery",
+              host_list_length: from_dns.length,
+              old_host_list_length: current.length
+            )
+            replace_hosts(from_dns)
+          else
+            ::Gitlab::Database::LoadBalancing::Logger.info(
+              event: :host_list_unchanged,
+              message: "Unchanged host list for service discovery",
+              host_list_length: from_dns.length,
+              old_host_list_length: current.length
+            )
+          end
 
           interval
         end