The new generation of cloud services such as AWS Lambda, Google Cloud Functions and Azure functions lower the bar for deploying responsive event-driven micro-services, auto-scaling web APIs, and high-performance web sites to the cloud. But with a major impact on architecture, these services also require teams to re-think how to approach sessions, storage, authorization and testing. This talk provides an experience report of moving a large collaboration platform from Heroku to AWS Lambda, leading to a huge improvement in scalability and performance, and a significant decrease in cost. You'll find out what worked well, where we got stuck, and how we made it work well at the end.