Try this way to provide database connection

db/post_migrate/20170206040400_remove_inactive_default_email_services.rb

@@ -31,13 +31,10 @@ class RemoveInactiveDefaultEmailServices < ActiveRecord::Migration
     end
   end
 
-  def with_connection
+  def with_connection(&block)
     pool = ActiveRecord::Base.establish_connection
-    connection = pool.connection
-
-    yield(connection)
-
+    pool.with_connection(&block)
   ensure
-    connection.close
+    pool.disconnect!
   end
 end