When Rendering Blocks: How Next.js Internals Stress the Node.js Event Loop

Last week, we talked about the complexity of running Next.js at enterprise scale. This week, we’re going under the hood — into the rendering engine itself. In this episode of The Node (& More) Banter, Luca Maraschi & Matteo Collina break down how Next.js’s server-side rendering model actually behaves inside Node.js — and why certain rendering patterns can silently overwhelm your event loop. We’ll explore: ✅ How SSR, RSC, streaming, and data-fetching all compete for the same event loop ✅ Why heavy render passes can starve I/O and cause tail latencies under load ✅ The real performance cost of React Server Components running inside Node.js ✅ Why some Next.js APIs behave like CPU workloads (even when they “feel” async) ✅ How cache misses, waterfalls, and rendering concurrency amplify Node.js pressure ✅ Techniques large-scale teams use to avoid event-loop saturation in production ✅ What observability actually looks like when your server is doing complex rendering If you’ve ever wondered why your Next.js app feels fast locally but bogs down under real traffic, this episode uncovers the part no framework abstracts away: rendering is work — and work competes for the event loop.