Server⁠-⁠side Rendering

Server-side Rendering, aka SSR, can be enabled in Astro. When you enable SSR you can:

Implement sessions for login state in your app.
Render data from an API called dynamically with fetch.@version 2.0.0
Deploy your site to a host using an adapter.

Enabling SSR in Your Project

To get started, enable SSR features in development mode with the output: server configuration option:

import { defineConfig } from 'astro/config';

export default defineConfig({
  output: 'server'
});

Adding an Adapter

When it’s time to deploy an SSR project, you also need to add an adapter. This is because SSR requires a server runtime: the environment that runs your server-side code. Each adapter allows Astro to output a script that runs your project on a specific runtime.

The following adapters are available today with more to come in the future:

`astro add` Install

You can add any of the official adapters 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. For example, to install the Netlify adapter, run:

npx astro add netlify

pnpm astro add netlify

yarn astro add netlify

Manual Install

You can also add an adapter manually by installing the package and updating astro.config.mjs yourself. (See the links above for adapter-specific instructions to complete the following two steps to enable SSR.) Using my-adapter as an example placeholder, the instructions will look something like:

Install the adapter to your project dependencies using your preferred package manager:
Terminal window

npm install @astrojs/my-adapter

Copied!
Terminal window

pnpm install @astrojs/my-adapter

Copied!
Terminal window

yarn add @astrojs/my-adapter

Copied!

Add the adapter to your astro.config.mjs file’s import and default export:

import { defineConfig } from 'astro/config';
import myAdapter from '@astrojs/my-adapter';

export default defineConfig({
  output: 'server',
  adapter: myAdapter(),
});

Features

Astro will remain a static-site generator by default. But once you enable a server-side rendering adapter, every route in your pages directory defaults to a server-rendered route and a few new features become available to you.

Hybrid Rendering

Added in: astro@2.0.0

Any individual page or server endpoint that supports exporting variables (.astro, .mdx, .ts, or .js) can opt in to pre-rendering when your Astro project is configured to use SSR with output: server. These files will be statically rendered at build-time, similar to the default output: static mode.

Simply add export const prerender = true:

---
export const prerender = true;
// ...
---
<html>
  <!-- Page here... -->
</html>

---
layout: '../layouts/markdown.astro'
title: 'My page'
---
export const prerender = true;

# This is my page

export const prerender = true;

export async function get() {
  return {
    body: JSON.stringify({ message: `This is my endpoint` }),
  };
}

Static pre-rendering by default

Added in: astro@2.5.0 New

You may have a site that is mostly static and can benefit from pre-rendering, but only a few of your pages or endpoints need to be server-rendered. SSR in Astro defaults to rendering on the server and requires you to individually designate the pages that should be static.

To avoid declaring most of your pages as pre-rendered, change the output from 'server' to 'hybrid' and take advantage of SSR with static pre-rendering by default:

export { defineConfig } from 'astro/config';

export default defineConfig({
  output: 'hybrid',
  experimental: {
    hybridOutput: true,
  },
});

With this configuration, all of your pages and API endpoints will be pre-rendered, even though your project is configured with an adapter to use SSR. You can then opt-out of pre-rendering any individual file or route by adding export const prerender = false to any files that should be server-rendered.

export const prerender = false;

export async function get() {
  let number = Math.random();
  return {
    body: JSON.stringify({ number, message: `Here's a random number: ${number}` }),
  };
}

`Astro.request.headers`

The headers for the request are available on Astro.request.headers. This works like the browser’s Request.headers. It is a Headers object, a Map-like object where you can retrieve headers such as the cookie.

---
const cookie = Astro.request.headers.get('cookie');
// ...
---
<html>
  <!-- Page here... -->
</html>

`Astro.request.method`

The HTTP method used in the request is available as Astro.request.method. This works like the browser’s Request.method. It returns the string representation of the HTTP method used in the request.

---
console.log(Astro.request.method) // GET (when navigated to in the browser)
---

`Astro.cookies`

This is a utility to read and modify a single cookie. It allows you to check, set, get and delete a cookie.

See more details about Astro.cookies and the AstroCookie type in the API reference.

The example below updates the value of a cookie for a page view counter.

---
let counter = 0

if(Astro.cookies.has("counter")){
  const cookie = Astro.cookies.get("counter")
  counter = cookie.number() + 1
}

Astro.cookies.set("counter",counter)

---
<html>
  <h1>Counter = {counter}</h1>
</html>

`Astro.redirect`

On the Astro global, this method allows you to redirect to another page. You might do this after checking if the user is logged in by getting their session from a cookie.

---
import { isLoggedIn } from '../utils';

const cookie = Astro.request.headers.get('cookie');

// If the user is not logged in, redirect them to the login page
if (!isLoggedIn(cookie)) {
  return Astro.redirect('/login');
}
---
<html>
  <!-- Page here... -->
</html>

`Response`

You can also return a Response from any page. You might do this to return a 404 on a dynamic page after looking up an id in the database.

---
import { getProduct } from '../api';

const product = await getProduct(Astro.params.id);

// No product found
if (!product) {
  return new Response(null, {
    status: 404,
    statusText: 'Not found'
  });
}
---
<html>
  <!-- Page here... -->
</html>

Server Endpoints

A server endpoint, also known as an API route, is a special function exported from a .js or .ts file within the src/pages/ folder. The function takes an endpoint context and returns a Response. A powerful feature of SSR, API routes are able to securely execute code on the server. To learn more, see our Endpoints Guide.

Streaming

Browsers natively support HTTP streaming, where a document is broken up into chunks, sent over the network in order, and rendered on the page in that order.

During this process, browsers consume HTML incrementally: parsing, rendering into the DOM, and painting. This happens whether or not you intentionally stream your HTML. Network conditions can cause large documents to be downloaded slowly, and waiting for data fetches can block page rendering.

Using streaming to improve page performance

The following page awaits some data in its frontmatter. Astro will wait for all of the fetch calls to resolve before sending any HTML to the browser.

---
const personResponse = await fetch('https://randomuser.me/api/');
const personData = await personResponse.json();
const randomPerson = personData.results[0];
const factResponse = await fetch('https://catfact.ninja/fact');
const factData = await factResponse.json();
---
<html>
  <head>
    <title>A name and a fact</title>
  </head>
  <body>
    <h2>A name</h2>
    <p>{randomPerson.name.first}</p>
    <h2>A fact</h2>
    <p>{factData.fact}</p>
  </body>
</html>

Moving the await calls into smaller components allows you to take advantage of Astro’s streaming. Using the following components to perform the data fetches, Astro can render some HTML first, such as the title, and then the paragraphs when the data is ready.

---
const personResponse = await fetch('https://randomuser.me/api/');
const personData = await personResponse.json();
const randomPerson = personData.results[0];
---
<p>{randomPerson.name.first}</p>

---
const factResponse = await fetch('https://catfact.ninja/fact');
const factData = await factResponse.json();
---
<p>{factData.fact}</p>

The Astro page below using these components can render parts of the page sooner. The <head>, <body>, and <h1> tags are no longer blocked by data fetches. The browser will then wait for RandomName to finish loading its Promises, and then send the resulting HTML over the network. It will render the next heading, and then it will wait for RandomFact and send its resulting HTML over the browser.

---
import RandomName from '../components/RandomName.astro'
import RandomFact from '../components/RandomFact.astro'
---
<html>
  <head>
    <title>A name and a fact</title>
  </head>
  <body>
    <h2>A name</h2>
    <RandomName />
    <h2>A fact</h2>
    <RandomFact />
  </body>
</html>

Including Promises directly

You can also include promises directly in the template. Instead of blocking the entire component, it will only block the markup that comes after it.

---
const personPromise = fetch('https://randomuser.me/api/')
  .then(resp => response.json())
  .then(arr => arr[0].name.first);
const factPromise = fetch('https://catfact.ninja/fact')
  .then(resp => response.json())
  .then(factData => factData.fact);
---
<html>
  <head>
    <title>A name and a fact</title>
  </head>
  <body>
    <h2>A name</h2>
    <p>{personPromise}</p>
    <h2>A fact</h2>
    <p>{factPromise}</p>
  </body>
</html>

In this example, A name will render while personPromise is loading. At that point, A fact will be appear, while factPromise is loading.

What’s on your mind?

What’s on your mind?

Server⁠-⁠side Rendering

Enabling SSR in Your Project

Adding an Adapter

`astro add` Install

Manual Install

Features

Hybrid Rendering

Static pre-rendering by default

`Astro.request.headers`

`Astro.request.method`

`Astro.cookies`

`Astro.redirect`

`Response`

Server Endpoints

Streaming

Using streaming to improve page performance

Including Promises directly

Enabling SSR in Your Project

Adding an Adapter

astro add Install

Manual Install

Features

Hybrid Rendering

Static pre-rendering by default

Astro.request.headers

Astro.request.method

Astro.cookies

Astro.redirect

Response

Server Endpoints

Streaming

Using streaming to improve page performance

Including Promises directly

`astro add` Install

`Astro.request.headers`

`Astro.request.method`

`Astro.cookies`

`Astro.redirect`

`Response`