What is Incremental Static Regeneration (ISR)?
ISR enables you to use static generation on a per-page basis while revalidating pages in the background as traffic comes in. Incremental Static Regeneration (ISR) enables you to:
- 1
Update static content without rebuilding the entire site
- 2
Reduce server load by serving prerendered, static pages for most requests
- 3
Ensure proper cache-control headers are automatically added to pages
- 4
Handle large amounts of content pages without long next build times
- 1
During next build, all known blog posts are generated (there are 25 in this example)
- 2
All requests made to these pages (e.g. /blog/1) are cached and instantaneous
- 3
After 60 seconds has passed, the next request will still show the cached (stale) page
- 4
The cache is invalidated and a new version of the page begins generating in the background
- 5
Once generated successfully, Next.js will display and cache the updated page
- 6
If /blog/26 is requested, Next.js will generate and cache this page on-demand
Scenario Questions
0-2 years experience
- 1How would you configure a Next.js page to use ISR with a revalidation time of 10 seconds?
- 2What does a user see when they request a page that is currently being regenerated by ISR?
- 3If you forget to export getStaticProps on a page you intended to use ISR, what will happen at runtime?
2-5 years experience
- 1Your product listing page uses ISR with revalidate: 60, but after a promotion ends users still see the old price. How would you investigate and fix it?
- 2Explain the trade‑offs between ISR and server‑side rendering for a dashboard that needs to refresh data every minute.
- 3After a recent deployment, ISR pages are no longer updating when the underlying content changes. What could be causing this behavior?
5-8 years experience
- 1Design a strategy that combines ISR with on‑demand revalidation so authors can publish blog updates instantly without a full redeploy.
- 2What performance impacts might you see if you set a very low revalidate interval on a page that calls an external API with strict rate limits?
- 3How would you set up monitoring and alerting to detect ISR regeneration failures in a large Next.js monorepo?
8+ years experience
- 1Your team is migrating a legacy e‑commerce platform to Next.js. How would you decide which pages get ISR, which stay SSR, and plan a phased rollout?
- 2Discuss cross‑team considerations when exposing an on‑demand ISR endpoint for content editors, including security, authentication, and rate‑limiting.
- 3At global scale, how would you architect the CDN and caching layers to ensure ISR works consistently across multiple regions and edge nodes?
Follow-up Questions
- What steps would you take to debug a page that is serving stale ISR content?
- Which metrics would you monitor to know ISR is working correctly at scale?
- How would you handle a situation where the external data source fails during regeneration?