Dynamically sets the database connection for Geo::BaseRegistry model

If Gitlab::Geo.secondary? changes, we need to reinitialize the  connection properly in the model to avoid requiring a full unicorn restart.

app/models/geo/base_registry.rb

 class Geo::BaseRegistry < ActiveRecord::Base
   self.abstract_class = true
 
-  if Gitlab::Geo.configured? && (Gitlab::Geo.secondary? || Rails.env.test?)
-    establish_connection Rails.configuration.geo_database
+  # If Gitlab::Geo.secondary? changes, we need to reinitialize the  connection
+  # properly in the model to avoid requiring a full unicorn restart.
+  def self.retrieve_connection
+    set_connection! if should_change_connection?
+    connection_handler.retrieve_connection(self)
+  end
+
+  private
+
+  def self.set_connection!
+    if Gitlab::Geo.tracking_connection_available?
+      establish_connection Rails.configuration.geo_database
+    else
+      establish_connection "#{Rails.env}".to_sym
+    end
+  end
+
+  def self.should_change_connection?
+    using_master_connection? && Gitlab::Geo.tracking_connection_available?
+  end
+
+  def self.using_master_connection?
+    master_connection   = ActiveRecord::Base.connection_config[:database]
+    tracking_connection = Geo::BaseRegistry.connection_config[:database]
+
+    master_connection === tracking_connection
   end
 end

lib/gitlab/geo.rb

@@ -46,6 +46,10 @@ def self.configured?
       Rails.configuration.respond_to?(:geo_database)
     end
 
+    def self.tracking_connection_available?
+      self.cache_value(:tracking_connection_available) { self.configured? && (self.secondary? || Rails.env.test?) }
+    end
+
     def self.license_allows?
       ::License.current&.feature_available?(:geo)
     end