Node servers

To generate a standalone Node server, use adapter-node.

Usage permalink

Install with npm i -D @sveltejs/adapter-node, then add the adapter to your svelte.config.js:

ts
import adapter from '@sveltejs/adapter-node';
Cannot find module '@sveltejs/adapter-node' or its corresponding type declarations.2307Cannot find module '@sveltejs/adapter-node' or its corresponding type declarations.

export default {
    kit: {
        adapter: adapter()
    }
};

Deploying permalink

First, build your app with npm run build. This will create the production server in the output directory specified in the adapter options, defaulting to build.

You will need the output directory, the project's package.json, and the production dependencies in node_modules to run the application. Production dependencies can be generated by copying the package.json and package-lock.json and then running npm ci --omit dev (you can skip this step if your app doesn't have any dependencies). You can then start your app with this command:

node build

Development dependencies will be bundled into your app using Rollup. To control whether a given package is bundled or externalised, place it in devDependencies or dependencies respectively in your package.json.

Environment variables permalink

In dev and preview, SvelteKit will read environment variables from your .env file (or .env.local, or .env.[mode], as determined by Vite.)

In production, .env files are not automatically loaded. To do so, install dotenv in your project...

npm install dotenv

...and invoke it before running the built app:

node build
node -r dotenv/config build

PORT and HOST permalink

By default, the server will accept connections on 0.0.0.0 using port 3000. These can be customised with the PORT and HOST environment variables:

HOST=127.0.0.1 PORT=4000 node build

ORIGIN, PROTOCOL_HEADER and HOST_HEADER permalink

HTTP doesn't give SvelteKit a reliable way to know the URL that is currently being requested. The simplest way to tell SvelteKit where the app is being served is to set the ORIGIN environment variable:

ORIGIN=https://my.site node build

# or e.g. for local previewing and testing
ORIGIN=http://localhost:3000 node build

With this, a request for the /stuff pathname will correctly resolve to https://my.site/stuff. Alternatively, you can specify headers that tell SvelteKit about the request protocol and host, from which it can construct the origin URL:

PROTOCOL_HEADER=x-forwarded-proto HOST_HEADER=x-forwarded-host node build

x-forwarded-proto and x-forwarded-host are de facto standard headers that forward the original protocol and host if you're using a reverse proxy (think load balancers and CDNs). You should only set these variables if your server is behind a trusted reverse proxy; otherwise, it'd be possible for clients to spoof these headers.

If adapter-node can't correctly determine the URL of your deployment, you may experience this error when using form actions:

Cross-site POST form submissions are forbidden

ADDRESS_HEADER and XFF_DEPTH permalink

The RequestEvent object passed to hooks and endpoints includes an event.getClientAddress() function that returns the client's IP address. By default this is the connecting remoteAddress. If your server is behind one or more proxies (such as a load balancer), this value will contain the innermost proxy's IP address rather than the client's, so we need to specify an ADDRESS_HEADER to read the address from:

ADDRESS_HEADER=True-Client-IP node build

Headers can easily be spoofed. As with PROTOCOL_HEADER and HOST_HEADER, you should know what you're doing before setting these.

If the ADDRESS_HEADER is X-Forwarded-For, the header value will contain a comma-separated list of IP addresses. The XFF_DEPTH environment variable should specify how many trusted proxies sit in front of your server. E.g. if there are three trusted proxies, proxy 3 will forward the addresses of the original connection and the first two proxies:

<client address>, <proxy 1 address>, <proxy 2 address>

Some guides will tell you to read the left-most address, but this leaves you vulnerable to spoofing:

<spoofed address>, <client address>, <proxy 1 address>, <proxy 2 address>

We instead read from the right, accounting for the number of trusted proxies. In this case, we would use XFF_DEPTH=3.

If you need to read the left-most address instead (and don't care about spoofing) — for example, to offer a geolocation service, where it's more important for the IP address to be real than trusted, you can do so by inspecting the x-forwarded-for header within your app.

BODY_SIZE_LIMIT permalink

The maximum request body size to accept in bytes including while streaming. Defaults to 512kb. You can disable this option with a value of 0 and implement a custom check in handle if you need something more advanced.

Options permalink

The adapter can be configured with various options:

ts
import adapter from '@sveltejs/adapter-node';
Cannot find module '@sveltejs/adapter-node' or its corresponding type declarations.2307Cannot find module '@sveltejs/adapter-node' or its corresponding type declarations.

export default {
    kit: {
        adapter: adapter({
            // default options are shown
            out: 'build',
            precompress: false,
            envPrefix: '',
            polyfill: true
        })
    }
};

out permalink

The directory to build the server to. It defaults to build — i.e. node build would start the server locally after it has been created.

precompress permalink

Enables precompressing using gzip and brotli for assets and prerendered pages. It defaults to false.

envPrefix permalink

If you need to change the name of the environment variables used to configure the deployment (for example, to deconflict with environment variables you don't control), you can specify a prefix:

ts
envPrefix: 'MY_CUSTOM_';

MY_CUSTOM_HOST=127.0.0.1 \
MY_CUSTOM_PORT=4000 \
MY_CUSTOM_ORIGIN=https://my.site \
node build

polyfill permalink

Controls whether your build will load polyfills for missing modules. It defaults to true, and should only be disabled when using Node 18.11 or greater.

Note: to use Node's built-in crypto global with Node 18 you will need to use the --experimental-global-webcrypto flag. This flag is not required with Node 20.

Custom server permalink

The adapter creates two files in your build directory — index.js.ts and handler.js.ts. Running index.js.ts — e.g. node build, if you use the default build directory — will start a server on the configured port.

Alternatively, you can import the handler.js.ts file, which exports a handler suitable for use with Express, Connect or Polka (or even just the built-in http.createServer) and set up your own server:

ts
import { handler } from './build/handler.js';
Cannot find module './build/handler.js' or its corresponding type declarations.2307Cannot find module './build/handler.js' or its corresponding type declarations.
import express from 'express';
Cannot find module 'express' or its corresponding type declarations.2307Cannot find module 'express' or its corresponding type declarations.

const app = express();

// add a route that lives separately from the SvelteKit app
app.get('/healthcheck', (req, res) => {
Parameter 'req' implicitly has an 'any' type.
Parameter 'res' implicitly has an 'any' type.7006
7006Parameter 'req' implicitly has an 'any' type.
Parameter 'res' implicitly has an 'any' type.
    res.end('ok');
});

// let SvelteKit handle everything else, including serving prerendered pages and static assets
app.use(handler);

app.listen(3000, () => {
    console.log('listening on port 3000');
});

Troubleshooting permalink

Is there a hook for cleaning up before the server exits? permalink

There's nothing built-in to SvelteKit for this, because such a cleanup hook depends highly on the execution environment you're on. For Node, you can use its built-in process.on(..) to implement a callback that runs before the server exits:

ts
function shutdownGracefully() {
    // anything you need to clean up manually goes in here
    db.shutdown();
Cannot find name 'db'.2304Cannot find name 'db'.
}

process.on('SIGINT', shutdownGracefully);
Cannot find name 'process'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.2580Cannot find name 'process'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
process.on('SIGTERM', shutdownGracefully);
Cannot find name 'process'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.2580Cannot find name 'process'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.