When deploying Astro with Vercel Edge, environment variables only work when they are prefixed with PUBLIC_.
You can see that in src/pages/index.astro.
To test this yourself:
- Fork this repo
- Create a new project on Vercel using this repo
- Add two environment variables to the Vercel project:
MY_ENV_VARPUBLIC_MY_ENV_VAR
After deploying, on the homepage you should see the MY_ENV_VAR variable is not working, but the PUBLIC_ one is.
Because Edge Functions are not client-side, it seems like this is a bug. You should be able to access things like database credentials inside an Edge function, without prefixing it with PUBLIC_.