Cache runtime routes (ISR)

[jbmoelker]

All HTML routes get a cache-control: public, max-age=0, must-revalidate header from Cloudflare. For our pages statically generated during build this is fine. Cloudflare's CDN and caching mechanism has us covered. For pages that are rendered during runtime the responses will be slower and will hit the underlying services (like DatoCMS) more. We can improve that performance by adding caching headers in an Incremental Static Rendering (ISR) pattern. This blog post explains this pattern using Astro and Cloudflare well: https://logsnag.com/blog/implementing-isr-in-astro

In short, on routes we want to add caching to we can do something like this:

---
// Set Cache-Control headers for CDN caching
Astro.response.headers.set('Cache-Control', 'public, s-maxage=60, stale-while-revalidate=30');
---

And we could add a helper to set that header (as lib or more conveniently on Astro.locals as we need access to the Astro object), like so: (Astro.locals.)setCache({ seconds: 60 }).