I would like to share our experiences while migrating a VM-based hosting infrastructure at Flying Circus Internet Operations from Gentoo to NixOS. It is a case study of migrating 500+ VM running diverse customer projects using a wide range of web technologies. I'll cover the following main points: 1. What was our motivation to change to NixOS? Which specific features of NixOS attracted us? 2. Creating a NixOS-based hosting platform - What did we have to implement? What is still missing? 3. What are the pain points? How could NixOS become more attractive? 4. What do our users think? -- benefits and stumbling blocks. --- Bio: Christian is a systems engineer working with Flying Circus Internet Operations in Halle (Saale), Germany. He works mainly on infrastructure which keeps customers' web applications running. Main programming languages are Python, Nix, Rust. Christian is a regular contributor to NixOS, most known for vulnix and vulnerability roundups.