Why Did We Rewrite Our Main Product Four Times? by Leon Hu "Hi, this is a friendly reminder you have an appt on 12/07, Thursday 2pm". How hard can building and scaling an Appointment Reminder system be? An average developer can build such proof of concept in under a day. But to scale it to sending to millions of patients a week, nobody in our team thought it'd take us to rewrite it the 4th time. From dealing performance pain and ever increasing complexity, we poured in countless hours to come up with the perfect design. We have a thing or two to share about solving a seemingly trivial problem.