What is Islands Architecture?
A rendering pattern where static server-rendered HTML contains isolated interactive components that hydrate independently.
Definition
Islands architecture, articulated by Katie Sylor-Miller and Jason Miller and implemented most visibly by Astro, treats a page as mostly static HTML dotted with self-contained interactive "islands"—a carousel, a cart button—each shipping and hydrating its own JavaScript. Unlike whole-app hydration in classic SSR frameworks, non-interactive markup never pays a JavaScript cost, and islands can hydrate lazily (Astro's client:visible defers until scrolled into view). Fresh (Deno) and Marko follow similar models, while Qwik's resumability pursues the same goal by other means. The result is drastically less shipped JavaScript for content-heavy sites where interactivity is sparse.