On the TeachersPayTeachers.com Engineering blog they've posted a retrospective of what they went through to scale to millions of views per day on AWS using Kubernetes, React, PHP, and Elixir.

Here at Teachers Pay Teachers (or TpT, as we call it) we’ve been in the process of migrating our website from a PHP monolith to a microservice based architecture utilizing React, Phoenix and GraphQL. To date, this migration has delighted our community of educators with it’s myriad of UX improvements. We’re able to objectively measure these improvements with our A/B testing infrastructure which also enables us to gradually expose functionality to broader and broader levels of traffic.

Our product page receives ~2 million pages views per day making it the most heavily trafficked page on TpT (here’s an example page). We decided to use a simple UI refresh as an opportunity to migrate the page to our new tech stack. This post dives deeply into the challenges we overcame while scaling the product page on our new infrastructure!

The post then shows an infographic of their migration and the major steps in the process along a timeline. They also include an overview of their updated architecture, specific technical issues found during the migration and handling server load. They also cover error spikes they saw just after scaling and how they were either able to resolve or just dismiss them as "red herrings".