If you wish to [use server-side rendering (SSR)](https://docs.astro.build/en/guides/server-side-rendering/), Astro requires an adapter that matches your deployment runtime.
[Vercel](https://www.vercel.com/) is a deployment platform that allows you to host your site by connecting directly to your GitHub repository. This adapter enhances the Astro build process to prepare your project for deployment through Vercel.
Add the Vercel adapter to enable SSR in your Astro project with the following `astro add` command. This will install the adapter and make the appropriate changes to your `astro.config.mjs` file in one step.
1. Install the Vercel adapter to your project’s dependencies using your preferred package manager. If you’re using npm or aren’t sure, run this in the terminal:
-`edge`: SSR inside an [Edge function](https://vercel.com/docs/concepts/functions/edge-functions).
-`serverless`: SSR inside a [Node.js function](https://vercel.com/docs/concepts/functions/serverless-functions).
-`static`: generates a static website following Vercel's output formats, redirects, etc.
> **Note**: deploying to the Edge has [its limitations](https://vercel.com/docs/concepts/functions/edge-functions#known-limitations). An edge function can't be more than 1 MB in size and they don't support native Node.js APIs, among others.
You can change where to target by changing the import:
You can deploy by CLI (`vercel deploy`) or by connecting your new repo in the [Vercel Dashboard](https://vercel.com/). Alternatively, you can create a production build locally:
> When building for the Edge, all the dependencies get bundled in a single file to save space. **No extra file will be bundled**. So, if you _need_ some file inside the function, you have to specify it in `includeFiles`.
You can use Vercel middleware to intercept a request and redirect before sending a response. Vercel middleware can run for Edge, SSR, and Static deployments. You don't need to install `@vercel/edge` to write middleware, but you do need to install it to use features such as geolocation. For more information see [Vercel’s middleware documentation](https://vercel.com/docs/concepts/functions/edge-middleware).
1. Add a `middleware.js` file to the root of your project:
```js
// middleware.js
export const config = {
// Only run the middleware on the admin route
matcher: '/admin',
};
export default function middleware(request) {
const url = new URL(request.url);
// You can retrieve IP location or cookies here.
if (url.pathname === "/admin") {
url.pathname = "/"
}
return Response.redirect(url);
}
```
1. While developing locally, you can run `vercel dev` to run middleware. In production, Vercel will handle this for you.
**A few known complex packages (example: [puppeteer](https://github.com/puppeteer/puppeteer)) do not support bundling and therefore will not work properly with this adapter.** By default, Vercel doesn't include npm installed files & packages from your project's `./node_modules` folder. To address this, the `@astrojs/vercel` adapter automatically bundles your final build output using `esbuild`.
