Incremental static regeneration (ISR)
Incremental static regeneration is the hybrid where pages are pre-rendered to static HTML but the framework refreshes them in the background after a defined revalidation period — combining SSG's first-byte speed with SSR's freshness. Used in Next.js, Astro, and others.
ISR is the pragmatic middle path between SSG and SSR. The model: on first request, the static HTML is served instantly; if the page is stale (older than the revalidate window), the framework triggers a background rebuild; the next request gets the fresh version. The user-perceived latency stays at SSG levels because no request waits for rebuild. ISR fits content that's mostly stable but occasionally updated: product pages, blog indexes, glossary terms. The trade-off: cache invalidation is eventual rather than immediate (the revalidate window is the eventual consistency floor); on-demand revalidation APIs address this by letting backend events trigger immediate rebuilds.
Related terms
- Static site generation (SSG)
Static site generation pre-renders every page to plain HTML at build time, then serves the HTML directly from a CDN with no server-side execution per request.
- Server-side rendering (SSR)
Server-side rendering generates the HTML for a page on the server per request — the response is fully-formed HTML that the browser can render immediately without waiting for client-side JavaScript.
- CDN edge
A CDN edge is one of the geographically distributed points-of-presence operated by a content delivery network — typically hundreds of locations worldwide where static and cacheable content is served from the location closest to the user.