At Twilio SendGrid, we rewrote and re-architected our main services while increasing our scale. We went from stateful Perl and Python to now mostly stateless Go

At Twilio SendGrid, we rewrote and re-architected our main services while increasing our scale. We went from stateful Perl and Python to now mostly stateless Go. It is very hard to do right. You have to find minimal changes that can have results compared for accuracy. It has literally taken us years to do so safely and we are still in flux. The change has been nothing but positive, but it is not something to take on lightly.