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
- Deploy your site to a host using an adapter.
Enabling SSR in Your ProjectSection titled Enabling SSR in Your Project
To get started, enable SSR features in development mode with the
output: server configuration option:
Adding an AdapterSection titled 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:
Section titled astro add Install
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:
Manual InstallSection titled 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:
Add the adapter to your
astro.config.mjsfile’s import and default export:
FeaturesSection titled 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 RenderingSection titled Hybrid Rendering
Any individual page or server endpoint that supports exporting variables (
.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.
export const prerender = true:
Static pre-rendering by defaultSection titled Static pre-rendering by default
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
'hybrid' and take advantage of SSR with static pre-rendering by default:
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.
Section titled 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.
Section titled 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.
Section titled 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.
Section titled Astro.redirect
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.
Section titled 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.
Server EndpointsSection titled Server Endpoints
A server endpoint, also known as an API route, is a special function exported from a
.ts file within the
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.
StreamingSection titled 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 performanceSection titled 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.
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.
The Astro page below using these components can render parts of the page sooner. The
<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.
Including Promises directlySection titled 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.
In this example,
A name will render while
personPromise is loading. At that point,
A fact will be appear, while
factPromise is loading.