Netflix runs hundreds of multivariate AB tests a year, many of which help personalize the experience in the UI. This causes an exponential growth in the number of user experiences we serve to members, with each unique experience resulting in a unique JS/CSS bundle. Pre-publishing million of permutations to the CDN for each build of each UI simply does not work at Netflix scale.
Instead, we've taken a novel approach by standing up a brand new Node.js service: Codex. Codex's sole responsibility is to build personalized JS/CSS bundles on the fly for our members as they move through the Netflix user experience. This frees up our UI teams to innovate rapidly on the UI itself, without having to worry about the costs of infrastructure and the complexity of pre-publishing to the CDN.
As we stood up Codex, we learned a ton about building a horizontally scalable Node.js microservice. This talk is the story of how we built, designed, and scaled that service to meet the needs of our 80 million customers.