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The Adapter API enables server-side rendering (SSR) for Astro by providing host-specific request handling and build configuration. Use this API to deploy Astro to any cloud provider or edge platform.

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When to use this API

Use the Adapter API when you need to:
  • Enable SSR deployment to a specific hosting platform
  • Configure build output for serverless functions
  • Handle platform-specific request/response formats
  • Set up preview servers for testing SSR builds
  • Implement host-specific features (edge middleware, image optimization, etc.)

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Creating an adapter

An adapter is a special integration that calls setAdapter() in the astro:config:done hook: 
export default function createAdapter() {
  return {
    name: '@example/my-adapter',
    hooks: {
      'astro:config:done': ({ setAdapter }) => {
        setAdapter({
          name: '@example/my-adapter',
          serverEntrypoint: '@example/my-adapter/server.js',
          supportedAstroFeatures: {
            staticOutput: 'stable'
          }
        });
      },
    },
  };
}

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Adapter configuration

The setAdapter() function accepts an object with the following properties:
​
name
string
required
Unique name for your adapter, used for logging.
​
serverEntrypoint
string | URL
required
Path to the server entrypoint file that handles rendering.
serverEntrypoint: '@example/my-adapter/server.js'
​
supportedAstroFeatures
AstroAdapterFeatureMap
Map of Astro features supported by the adapter. This allows Astro to provide appropriate error messages.Available features:
  • staticOutput - Serve static pages
  • hybridOutput - Mix of static and SSR pages
  • serverOutput - All pages rendered on-demand
  • i18nDomains - i18n domain support
  • envGetSecret - astro:env/server secret support
  • sharpImageService - Sharp image service support
Each feature accepts a support level:
  • 'stable' - Fully supported
  • 'experimental' - Supported but may change
  • 'limited' - Partial support
  • 'deprecated' - Supported but will be removed
  • 'unsupported' - Not supported
supportedAstroFeatures: {
  staticOutput: 'stable',
  hybridOutput: 'experimental',
  serverOutput: 'stable',
  i18nDomains: 'unsupported'
}
​
adapterFeatures
AstroAdapterFeatures
Adapter-specific features that change build output:
{
  edgeMiddleware?: boolean;
  buildOutput?: 'static' | 'server';
  experimentalStaticHeaders?: boolean;
}
​
args
any
JSON-serializable value passed to the server entrypoint at runtime. Useful for build-time configuration.
args: {
  assets: config.build.assets,
  serverPath: '/api'
}
​
exports
string[]
Array of named exports from your server entrypoint’s createExports() function.
exports: ['handler', 'middleware']
​
previewEntrypoint
string | URL
Path to a module that starts the preview server when running astro preview.
previewEntrypoint: '@example/my-adapter/preview.js'

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Building a server entrypoint

The server entrypoint handles rendering at request time. It must export either createExports() or start().

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createExports()

Export a function that returns the exports required by your host: 
import { App } from 'astro/app';

export function createExports(manifest, args) {
  const app = new App(manifest);
  
  const handler = async (request, context) => {
    return await app.render(request);
  };
  
  return { handler };
}
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manifest
SSRManifest
required
The SSR manifest containing routing and build information.
​
args
any
The args object defined in your adapter configuration.

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start()

For hosts that require you to start the server (e.g., listening to a port): 
import { App } from 'astro/app';

export function start(manifest, args) {
  const app = new App(manifest);
  
  addEventListener('fetch', event => {
    event.respondWith(app.render(event.request));
  });
}

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The App class

Imported from astro/app, the App class provides methods for rendering: 
import { App } from 'astro/app';

const app = new App(manifest);

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app.render()

Renders a page and returns a Response: 
app.render(
  request: Request,
  options?: RenderOptions
): Promise<Response>
​
request
Request
required
Standard Request object to render.
​
options
RenderOptions
Optional rendering configuration:
{
  addCookieHeader?: boolean;
  clientAddress?: string;
  locals?: object;
  routeData?: RouteData;
}
Example: 
const response = await app.render(request, {
  clientAddress: request.headers.get('x-forwarded-for'),
  locals: { user: authenticatedUser }
});

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app.match()

Determines if a request matches Astro’s routing rules: 
app.match(
  request: Request,
  allowPrerenderedRoutes?: boolean
): RouteData | undefined

if (app.match(request)) {
  return await app.render(request);
} else {
  return new Response('Not Found', { status: 404 });
}

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Static methods

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App.getSetCookieFromResponse
(response: Response) => Generator<string>
Returns individual cookie header values from a response.
for (const cookie of App.getSetCookieFromResponse(response)) {
  response.headers.append('Set-Cookie', cookie);
}
​
App.validateForwardedHost
(forwardedHost: string, allowedDomains?: RemotePattern[], protocol?: string) => boolean
Validates a forwarded host against allowed domains.
const forwardedHost = request.headers.get('X-Forwarded-Host');
if (App.validateForwardedHost(forwardedHost, manifest.allowedDomains)) {
  // Process request
}

​
Node.js adapter features

For Node.js environments, use astro/app/node: 
import { NodeApp } from 'astro/app/node';

const nodeApp = new NodeApp(manifest);

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NodeApp.createRequest()

Converts Node’s IncomingMessage to a standard Request: 
import { createServer } from 'node:http';
import { NodeApp } from 'astro/app/node';

const server = createServer(async (req, res) => {
  const request = NodeApp.createRequest(req);
  const response = await app.render(request);
  await NodeApp.writeResponse(response, res);
});

​
NodeApp.writeResponse()

Streams a Response to Node’s ServerResponse: 
const response = await app.render(request);
await NodeApp.writeResponse(response, res);

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Feature support configuration

Define support levels for Astro features: 
supportedAstroFeatures: {
  staticOutput: 'stable',
  hybridOutput: 'stable',
  serverOutput: 'stable',
  i18nDomains: {
    support: 'limited',
    message: 'Domain routing requires manual DNS configuration'
  },
  envGetSecret: 'stable',
  sharpImageService: 'experimental'
}
Provide custom messages for non-stable support: 
sharpImageService: {
  support: 'experimental',
  message: 'Sharp support is experimental. Some features may not work.'
}

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Adapter features

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edgeMiddleware

Prevents middleware from being bundled with every page: 
adapterFeatures: {
  edgeMiddleware: true
}
Access the middleware entry point in astro:build:ssr: 
'astro:build:ssr': ({ middlewareEntryPoint }) => {
  if (middlewareEntryPoint) {
    // Bundle middleware separately
  }
}

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buildOutput

Force a specific build output type: 
adapterFeatures: {
  buildOutput: 'static' // or 'server'
}

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Example adapter

// my-adapter.mjs
export default function createAdapter() {
  return {
    name: '@example/my-adapter',
    hooks: {
      'astro:config:done': ({ config, setAdapter }) => {
        setAdapter({
          name: '@example/my-adapter',
          serverEntrypoint: '@example/my-adapter/server.js',
          supportedAstroFeatures: {
            staticOutput: 'stable',
            serverOutput: 'stable',
            hybridOutput: 'stable'
          },
          args: {
            deploymentId: process.env.DEPLOYMENT_ID
          },
          exports: ['handler']
        });
      },
      'astro:build:done': ({ logger }) => {
        logger.info('Build complete! Deploy to your platform.');
      }
    }
  };
}

// server.js
import { App } from 'astro/app';

export function createExports(manifest, args) {
  const app = new App(manifest);
  
  const handler = async (request) => {
    const clientAddress = request.headers.get('x-forwarded-for');
    const response = await app.render(request, { clientAddress });
    return response;
  };
  
  return { handler };
}