diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 519acd7605ae9c90900e7b61baf9d53c42f6ef7d..84604452f7b859942424e354284f2e360a2efb5a 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -125,6 +125,10 @@ def self.configurations
 
       mattr_accessor :connection_handlers, instance_accessor: false, default: {}
 
+      mattr_accessor :writing_role, instance_accessor: false, default: :writing
+
+      mattr_accessor :reading_role, instance_accessor: false, default: :reading
+
       class_attribute :default_connection_handler, instance_writer: false
 
       self.filter_attributes = []
@@ -138,7 +142,6 @@ def self.connection_handler=(handler)
       end
 
       self.default_connection_handler = ConnectionAdapters::ConnectionHandler.new
-      self.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
     end
 
     module ClassMethods
diff --git a/activerecord/lib/active_record/middleware/database_selector/resolver.rb b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
index acdb9b32388e703e7bbbfe929e7fa3826da31bb0..fc71835cea04cdbe4ad1a4738ebddcec8da8d517 100644
--- a/activerecord/lib/active_record/middleware/database_selector/resolver.rb
+++ b/activerecord/lib/active_record/middleware/database_selector/resolver.rb
@@ -45,7 +45,7 @@ def write(&blk)
 
           def read_from_primary(&blk)
             ActiveRecord::Base.connection.while_preventing_writes do
-              ActiveRecord::Base.connected_to(role: :writing) do
+              ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
                 instrumenter.instrument("database_selector.active_record.read_from_primary") do
                   yield
                 end
@@ -54,7 +54,7 @@ def read_from_primary(&blk)
           end
 
           def read_from_replica(&blk)
-            ActiveRecord::Base.connected_to(role: :reading) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.reading_role) do
               instrumenter.instrument("database_selector.active_record.read_from_replica") do
                 yield
               end
@@ -62,7 +62,7 @@ def read_from_replica(&blk)
           end
 
           def write_to_primary(&blk)
-            ActiveRecord::Base.connected_to(role: :writing) do
+            ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
               instrumenter.instrument("database_selector.active_record.wrote_to_primary") do
                 yield
               ensure
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index a981fa97d90d53141116b7f57e147204f3118f95..f0b5ab2f087c4e467a2ffa39d5904c278ec8b22a 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -197,6 +197,7 @@ class Railtie < Rails::Railtie # :nodoc:
     # and then establishes the connection.
     initializer "active_record.initialize_database" do
       ActiveSupport.on_load(:active_record) do
+        self.connection_handlers = { writing_role => ActiveRecord::Base.default_connection_handler }
         self.configurations = Rails.application.config.database_configuration
         establish_connection
       end
diff --git a/activerecord/test/cases/connection_adapters/connection_handler_test.rb b/activerecord/test/cases/connection_adapters/connection_handler_test.rb
index 51d0cc3d12513472f4010dbf5f26f6449d65fa95..6282759a108efc0a7f2131d230be648b45873040 100644
--- a/activerecord/test/cases/connection_adapters/connection_handler_test.rb
+++ b/activerecord/test/cases/connection_adapters/connection_handler_test.rb
@@ -382,6 +382,11 @@ def test_remove_connection_should_not_remove_parent
           assert_not_nil ActiveRecord::Base.connection
           assert_same klass2.connection, ActiveRecord::Base.connection
         end
+
+        def test_default_handlers_are_writing_and_reading
+          assert_equal :writing, ActiveRecord::Base.writing_role
+          assert_equal :reading, ActiveRecord::Base.reading_role
+        end
       end
     end
   end
diff --git a/activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb b/activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb
index 8988755d24cf786d42e3c60b1c3ea8e36589328a..36591097b6b62c894ecbdfe419b1c7c493a3b862 100644
--- a/activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb
+++ b/activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb
@@ -126,6 +126,30 @@ def test_switching_connections_via_handler
           ENV["RAILS_ENV"] = previous_env
         end
 
+        def test_establish_connection_using_3_levels_config_with_non_default_handlers
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+          config = {
+            "default_env" => {
+              "readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" },
+              "primary"  => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" }
+            }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.connects_to(database: { default: :primary, readonly: :readonly })
+
+          assert_not_nil pool = ActiveRecord::Base.connection_handlers[:default].retrieve_connection_pool("primary")
+          assert_equal "db/primary.sqlite3", pool.spec.config[:database]
+
+          assert_not_nil pool = ActiveRecord::Base.connection_handlers[:readonly].retrieve_connection_pool("primary")
+          assert_equal "db/readonly.sqlite3", pool.spec.config[:database]
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ActiveRecord::Base.establish_connection(:arunit)
+          ENV["RAILS_ENV"] = previous_env
+        end
+
         def test_switching_connections_with_database_url
           previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
           previous_url, ENV["DATABASE_URL"] = ENV["DATABASE_URL"], "postgres://localhost/foo"
@@ -344,6 +368,24 @@ def test_calling_connected_to_on_a_non_existent_handler_raises
 
         assert_equal "No connection pool with 'primary' found for the 'reading' role.", error.message
       end
+
+      def test_default_handlers_are_writing_and_reading
+        assert_equal :writing, ActiveRecord::Base.writing_role
+        assert_equal :reading, ActiveRecord::Base.reading_role
+      end
+
+      def test_an_application_can_change_the_default_handlers
+        old_writing = ActiveRecord::Base.writing_role
+        old_reading = ActiveRecord::Base.reading_role
+        ActiveRecord::Base.writing_role = :default
+        ActiveRecord::Base.reading_role = :readonly
+
+        assert_equal :default, ActiveRecord::Base.writing_role
+        assert_equal :readonly, ActiveRecord::Base.reading_role
+      ensure
+        ActiveRecord::Base.writing_role = old_writing
+        ActiveRecord::Base.reading_role = old_reading
+      end
     end
   end
 end
diff --git a/activerecord/test/support/connection.rb b/activerecord/test/support/connection.rb
index 2a4fa53460b7f48177fcad546e23132baaa21227..367309dd85a89d538373e79c06850b08cb3972c8 100644
--- a/activerecord/test/support/connection.rb
+++ b/activerecord/test/support/connection.rb
@@ -21,6 +21,7 @@ def self.connection_config
   def self.connect
     puts "Using #{connection_name}"
     ActiveRecord::Base.logger = ActiveSupport::Logger.new("debug.log", 0, 100 * 1024 * 1024)
+    ActiveRecord::Base.connection_handlers = { ActiveRecord::Base.writing_role => ActiveRecord::Base.default_connection_handler }
     ActiveRecord::Base.configurations = connection_config
     ActiveRecord::Base.establish_connection :arunit
     ARUnit2Model.establish_connection :arunit2