DateTime.now and DateTime.current in Rails

One of our back-end test failed in the CI pipeline today. Which looks really weird since nobody touches that related code for a while so it’s probably not a regression.

After digging into the issue and we finally found the root cause: DateTime.now returns a DateTime object with system timezone instead of the timezone set in Rails application. This isn’t a big deal in most cases but can really cause troubles when you are calculating certain time. In our case, we were adding 2.years to the time and it happens that it could be 2020-02-29 instead of 2020-03-01 in different timezone (Leap year! Surprise! And this happens once every four years!).

Rails has already solved the above issue by patching a DateTime.current method. This method returns the current time with the correct timezone set in Rails.

So, in short, always use DateTime.current in your Rails application.