Astro + Vercel: Choosing static vs hybrid output for low‑traffic cost reduction

Goal: Minimize compute costs for a low‑traffic site

An Astro project is deployed to Vercel. The site contains a handful of dynamic pages that require server‑side rendering, but the majority of content is static. The objective is to keep monthly compute usage (and thus cost) as low as possible while still supporting the dynamic routes.

Astro offers two output modes:

• output: "static" – fully static build, no runtime required.
• output: "hybrid" – mix of static pages and SSR routes.

Vercel charges per serverless function invocation and per execution time. The question is how to configure the Astro project so that the dynamic routes incur minimal invocation cost while the static content remains free.

Key constraints:

• The ratio of dynamic to static pages is low (≈5%).
• Build times should stay within free-tier CI limits.
• Serverless runtime must be compatible with Vercel’s adapter.

Unresolved Questions

1. What is the most cost‑effective way to mark only the truly dynamic pages for SSR in a hybrid Astro project on Vercel?
2. How does the number of SSR routes affect Vercel’s compute cost, and is there a breakpoint where static pre‑rendering becomes cheaper?
3. Can Astro’s prerender flag be used to selectively pre‑render pages that would otherwise be SSR, and what impact does that have on build time versus runtime cost?