On-demand Rendering
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Astro allows you to choose on-demand rendering for some, or all of your pages and endpoints.
Generating HTML pages on the server when requested and sending them to the client is also known as server-side rendering (SSR). An adapter is used to run your project on the server and handle these requests.
Official Adapters
Section titled Official AdaptersAstro maintains official adapters for Node.js, Vercel, Netlify, and Cloudflare.
Find even more community-maintained adapters (e.g. Deno, SST, AWS) in our integrations directory.
Adaptateurs SSR
Add an Adapter
Section titled Add an AdapterTo render any of your pages on demand, for any output
mode, you need to add an adapter.
Each adapter allows Astro to output a script that runs your project on a specific runtime: the environment that runs code on the server to generate pages when they are requested (e.g. Netlify, Cloudflare).
You can find both official and community adapters in our integrations directory. Choose the one that corresponds to your deployment environment.
You can add any of the official adapters maintained by Astro 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:
You can also add an adapter manually by installing the NPM package (e.g. @astrojs/netlify
) and updating astro.config.mjs
yourself.
Note that different adapters may have different configuration settings. Read each adapter’s documentation, and apply any necessary config options to your chosen adapter in astro.config.mjs
Opting out of prerendering in static
mode
Section titled Opting out of prerendering in static modeFor a mostly static site configured as output: static
(Astro’s default), add export const prerender = false
to any files that should be server-rendered on demand:
Opting in to prerendering in server
mode
Section titled Opting in to prerendering in server modeWith output: server
configured, add export const prerender = true
to any page or route to prerender a static page or endpoint:
On-demand rendering features
Section titled On-demand rendering featuresHTML streaming
Section titled HTML streamingWith HTML streaming, a document is broken up into chunks, sent over the network in order, and rendered on the page in that order. Astro uses HTML streaming in on-demand rendering to send each component to the browser as it renders them. This makes sure the user sees your HTML as fast as possible, although network conditions can cause large documents to be downloaded slowly, and waiting for data fetches can block page rendering.
Features that modify the Response headers are only available at the page level. (You can’t use them inside of components, including layout components.) By the time Astro runs your component code, it has already sent the Response headers and they cannot be modified.
Cookies
Section titled CookiesA page or API endpoint rendered on demand can check, set, get, and delete cookies.
The example below updates the value of a cookie for a page view counter:
See more details about Astro.cookies
and the AstroCookie
type in the API reference.
Response
Section titled ResponseAstro.response
is a standard ResponseInit
object. It can be used to set the response status and headers.
The example below sets a response status and status text for a product listing page when the product does not exist:
Astro.response.headers
Section titled Astro.response.headersYou can set headers using the Astro.response.headers
object:
Return a Response
object
Section titled Return a Response objectYou can also return a Response object directly from any page using on-demand rendering.
The example below returns a 404 on a dynamic page after looking up an ID in the database:
Request
Section titled RequestAstro.request
is a standard Request object. It can be used to get the url
, headers
, method
, and even the body of the request.
You can access additional information from this object for pages that are not statically generated.
Astro.request.headers
Section titled Astro.request.headersThe headers for the request are available on Astro.request.headers
. This works like the browser’s Request.headers
. It is a Headers object where you can retrieve headers such as the cookie.
Astro.request.method
Section titled Astro.request.methodThe 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.
See more details about Astro.request
in the API reference.
Server Endpoints
Section titled Server EndpointsA server endpoint, also known as an API route, is a special function exported from a .js
or .ts
file within the src/pages/
folder. A powerful feature of server-side rendering on demand, API routes are able to securely execute code on the server.
The function takes an endpoint context and returns a Response.
To learn more, see our Endpoints Guide.
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