If you're using Astro as a static site builder—its behavior out of the box—you don't need an adapter.
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.
[Netlify](https://www.netlify.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 Netlify.
Add the Netlify 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 Netlify 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:
Netlify has two serverless platforms, [Netlify Functions](https://docs.netlify.com/functions/overview/) and [Netlify Edge Functions](https://docs.netlify.com/edge-functions/overview/). With Edge Functions your code is distributed closer to your users, lowering latency.
When deploying to Netlify Functions, you can choose to use an Edge Function to run your Astro middleware.
To enable this, set the `build.excludeMiddleware` Astro config option to `true`:
```js ins={9}
// astro.config.mjs
import { defineConfig } from 'astro/config';
import netlify from '@astrojs/netlify/functions';
export default defineConfig({
output: 'server',
adapter: netlify(),
build: {
excludeMiddleware: true,
},
});
```
#### Pass edge context to your site
Netlify Edge Functions provide a [context object](https://docs.netlify.com/edge-functions/api/#netlify-specific-context-object) including metadata about the request, such as a user’s IP, geolocation data, and cookies.
To expose values from this context to your site, create a `netlify-edge-middleware.ts` (or `.js`) file in your project’s [source directory](https://docs.astro.build/en/reference/configuration-reference/#srcdir). This file must export a function that returns the data to add to [Astro’s `locals` object](https://docs.astro.build/en/guides/middleware/#locals), which is available in middleware and Astro routes.
In this example, `visitorCountry` and `hasEdgeMiddleware` would both be added to Astro’s `locals` object:
```ts
// src/netlify-edge-middleware.ts
import type { Context } from 'https://edge.netlify.com';
// Return serializable data to add to Astro.locals
return {
visitorCountry: context.geo.country.name,
hasEdgeMiddleware: true,
};
}
```
> **Note**
> Netlify Edge Functions run in [a Deno environment](https://docs.netlify.com/edge-functions/api/#runtime-environment), so import statements in this file must use Deno’s URL syntax.
`netlify-edge-middleware.ts` must provide a function as its default export. This function:
- must return a JSON-serializable object, which cannot include types like `Map`, `function`, `Set`, etc.
- will always run first, before any other middleware and routes.
The Netlify adapter builds to a single function by default. Astro 2.7 added support for splitting your build into separate entry points per page. If you use this configuration, the Netlify adapter will generate a separate function for each page. This can help reduce the size of each function so they are only bundling code used on that page.
For static sites you usually don't need an adapter. However, if you use `redirects` configuration in your Astro config, the Netlify adapter can be used to translate this to the proper `_redirects` format.
> You can still include a `public/_redirects` file for manual redirects. Any redirects you specify in the redirects config are appended to the end of your own.
[Netlify On-demand Builders](https://docs.netlify.com/configure-builds/on-demand-builders/) are serverless functions used to generate web content as needed that’s automatically cached on Netlify’s Edge CDN. You can enable these functions using the [`builders` configuration](#builders).
By default, all pages will be rendered on first visit and the rendered result will be reused for every subsequent visit until you redeploy. To set a revalidation time, call the [`runtime.setBuildersTtl(ttl)` local](https://docs.astro.build/en/guides/middleware/#locals) with the duration (in seconds).
As an example, for the following snippet, Netlify will store the rendered HTML for 45 seconds.
```astro
---
import Layout from '../components/Layout.astro';
if (import.meta.env.PROD) {
Astro.locals.runtime.setBuildersTtl(45);
}
---
<Layouttitle="Astro on Netlify">
{new Date(Date.now())}
</Layout>
```
It is important to note that On-demand Builders ignore query params when checking for cached pages. For example, if `example.com/?x=y` is cached, it will be served for `example.com/?a=b` (different query params) and `example.com/` (no query params) as well.
After [performing a build](https://docs.astro.build/en/guides/deploy/#building-your-site-locally) the `netlify/` folder will contain [Netlify Functions](https://docs.netlify.com/functions/overview/) in the `netlify/functions/` folder.
The [Netlify Blog post on Astro](https://www.netlify.com/blog/how-to-deploy-astro/) and the [Netlify Documentation](https://docs.netlify.com/integrations/frameworks/astro/) provide more information on how to use this integration to deploy to Netlify.
Netlify Functions requires binary data in the `body` to be base64 encoded. The `@astrojs/netlify/functions` adapter handles this automatically based on the `Content-Type` header.
We check for common mime types for audio, image, and video files. To include specific mime types that should be treated as binary data, include the `binaryMediaTypes` option with a list of binary mime types.
- [Browse Astro Netlify projects on GitHub](https://github.com/search?q=path%3A**%2Fastro.config.mjs+%40astrojs%2Fnetlify&type=code) for more examples!
