---
title: Node servers
---

To generate a standalone Node server, use [`adapter-node`](https://github.com/sveltejs/kit/tree/main/packages/adapter-node).

## Usage

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

```js
// @errors: 2307
/// file: svelte.config.js
import adapter from '@sveltejs/adapter-node';

/** @type {import('@sveltejs/kit').Config} */
const config = {
	kit: {
		adapter: adapter()
	}
};

export default config;
```

## Deploying

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:

```sh
node build
```

Development dependencies will be bundled into your app using [Rollup](https://rollupjs.org). To control whether a given package is bundled or externalised, place it in `devDependencies` or `dependencies` respectively in your `package.json`.

### Compressing responses

You will typically want to compress responses coming from the server. If you're already deploying your server behind a reverse proxy for SSL or load balancing, it typically results in better performance to also handle compression at that layer since Node.js is single-threaded.

However, if you're building a [custom server](#Custom-server) and do want to add a compression middleware there, note that we would recommend using [`@polka/compression`](https://www.npmjs.com/package/@polka/compression) since SvelteKit streams responses and the more popular `compression` package does not support streaming and may cause errors when used.

## Environment variables

In `dev` and `preview`, SvelteKit will read environment variables from your `.env` file (or `.env.local`, or `.env.[mode]`, [as determined by Vite](https://vitejs.dev/guide/env-and-mode.html#env-files).)

In production, `.env` files are _not_ automatically loaded. To do so, install `dotenv` in your project...

```sh
npm install dotenv
```

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

```sh
node +++-r dotenv/config+++ build
```

If you use Node.js v20.6+, you can use the [`--env-file`](https://nodejs.org/en/learn/command-line/how-to-read-environment-variables-from-nodejs) flag instead:

```sh
node +++--env-file=.env+++ build
```

### `PORT`, `HOST` and `SOCKET_PATH`

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:

```sh
HOST=127.0.0.1 PORT=4000 node build
```

Alternatively, the server can be configured to accept connections on a specified socket path. When this is done using the `SOCKET_PATH` environment variable, the `HOST` and `PORT` environment variables will be disregarded.

```sh
SOCKET_PATH=/tmp/socket node build
```

### `ORIGIN`, `PROTOCOL_HEADER`, `HOST_HEADER`, and `PORT_HEADER`

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:

```sh
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:

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

> [!NOTE] [`x-forwarded-proto`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-Proto) and [`x-forwarded-host`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/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 you're hosting your proxy on a non-standard port and your reverse proxy supports `x-forwarded-port`, you can also set `PORT_HEADER=x-forwarded-port`.

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

> [!NOTE] Cross-site POST form submissions are forbidden

### `ADDRESS_HEADER` and `XFF_DEPTH`

The [`RequestEvent`](@sveltejs-kit#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:

```sh
ADDRESS_HEADER=True-Client-IP node build
```

> [!NOTE] Headers can easily be spoofed. As with `PROTOCOL_HEADER` and `HOST_HEADER`, you should [know what you're doing](https://adam-p.ca/blog/2022/03/x-forwarded-for/) 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](https://adam-p.ca/blog/2022/03/x-forwarded-for/):

```
<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`.

> [!NOTE] 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`

The maximum request body size to accept in bytes including while streaming. The body size can also be specified with a unit suffix for kilobytes (`K`), megabytes (`M`), or gigabytes (`G`). For example, `512K` or `1M`. Defaults to 512kb. You can disable this option with a value of `Infinity` (0 in older versions of the adapter) and implement a custom check in [`handle`](hooks#handle) if you need something more advanced.

### `SHUTDOWN_TIMEOUT`

The number of seconds to wait before forcefully closing any remaining connections after receiving a `SIGTERM` or `SIGINT` signal. Defaults to `30`. Internally the adapter calls [`closeAllConnections`](https://nodejs.org/api/http.html#servercloseallconnections). See [Graceful shutdown](#Graceful-shutdown) for more details.

### `IDLE_TIMEOUT`

When using systemd socket activation, `IDLE_TIMEOUT` specifies the number of seconds after which the app is automatically put to sleep when receiving no requests. If not set, the app runs continuously. See [Socket activation](#Socket-activation) for more details.

### `KEEP_ALIVE_TIMEOUT` and `HEADERS_TIMEOUT`

The number of seconds for [`keepAliveTimeout`](https://nodejs.org/api/http.html#serverkeepalivetimeout) and [`headersTimeout`](https://nodejs.org/api/http.html#serverheaderstimeout).

## Options

The adapter can be configured with various options:

```js
// @errors: 2307
/// file: svelte.config.js
import adapter from '@sveltejs/adapter-node';

/** @type {import('@sveltejs/kit').Config} */
const config = {
	kit: {
		adapter: adapter({
			// default options are shown
			out: 'build',
			precompress: true,
			envPrefix: ''
		})
	}
};

export default config;
```

### out

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

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

### envPrefix

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:

```js
envPrefix: 'MY_CUSTOM_';
```

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

## Graceful shutdown

By default `adapter-node` gracefully shuts down the HTTP server when a `SIGTERM` or `SIGINT` signal is received. It will:

1. reject new requests ([`server.close`](https://nodejs.org/api/http.html#serverclosecallback))
2. wait for requests that have already been made but not received a response yet to finish and close connections once they become idle ([`server.closeIdleConnections`](https://nodejs.org/api/http.html#servercloseidleconnections))
3. and finally, close any remaining connections that are still active after [`SHUTDOWN_TIMEOUT`](#Environment-variables-SHUTDOWN_TIMEOUT) seconds. ([`server.closeAllConnections`](https://nodejs.org/api/http.html#servercloseallconnections))

> [!NOTE] If you want to customize this behaviour you can use a [custom server](#Custom-server).

You can listen to the `sveltekit:shutdown` event which is emitted after the HTTP server has closed all connections. Unlike Node's `exit` event, the `sveltekit:shutdown` event supports asynchronous operations and is always emitted when all connections are closed even if the server has dangling work such as open database connections.

```js
// @errors: 2304
process.on('sveltekit:shutdown', async (reason) => {
  await jobs.stop();
  await db.close();
});
```

The parameter `reason` has one of the following values:

- `SIGINT` - shutdown was triggered by a `SIGINT` signal
- `SIGTERM` - shutdown was triggered by a `SIGTERM` signal
- `IDLE` - shutdown was triggered by [`IDLE_TIMEOUT`](#Environment-variables-IDLE_TIMEOUT)

## Socket activation

Most Linux operating systems today use a modern process manager called systemd to start the server and run and manage services. You can configure your server to allocate a socket and start and scale your app on demand. This is called [socket activation](https://0pointer.de/blog/projects/socket-activated-containers.html). In this case, the OS will pass two environment variables to your app — `LISTEN_PID` and `LISTEN_FDS`. The adapter will then listen on file descriptor 3 which refers to a systemd socket unit that you will have to create.

> [!NOTE] You can still use [`envPrefix`](#Options-envPrefix) with systemd socket activation. `LISTEN_PID` and `LISTEN_FDS` are always read without a prefix.

To take advantage of socket activation follow these steps.

1. Run your app as a [systemd service](https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html). It can either run directly on the host system or inside a container (using Docker or a systemd portable service for example). If you additionally pass an [`IDLE_TIMEOUT`](#Environment-variables-IDLE_TIMEOUT) environment variable to your app it will gracefully shutdown if there are no requests for `IDLE_TIMEOUT` seconds. systemd will automatically start your app again when new requests are coming in.

```ini
/// file: /etc/systemd/system/myapp.service
[Service]
Environment=NODE_ENV=production IDLE_TIMEOUT=60
ExecStart=/usr/bin/node /usr/bin/myapp/build
```

2. Create an accompanying [socket unit](https://www.freedesktop.org/software/systemd/man/latest/systemd.socket.html). The adapter only accepts a single socket.

```ini
/// file: /etc/systemd/system/myapp.socket
[Socket]
ListenStream=3000

[Install]
WantedBy=sockets.target
```

3. Make sure systemd has recognised both units by running `sudo systemctl daemon-reload`. Then enable the socket on boot and start it immediately using `sudo systemctl enable --now myapp.socket`. The app will then automatically start once the first request is made to `localhost:3000`.

## Custom server

The adapter creates two files in your build directory — `index.js` and `handler.js`. Running `index.js` — 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` file, which exports a handler suitable for use with [Express](https://github.com/expressjs/express), [Connect](https://github.com/senchalabs/connect) or [Polka](https://github.com/lukeed/polka) (or even just the built-in [`http.createServer`](https://nodejs.org/dist/latest/docs/api/http.html#httpcreateserveroptions-requestlistener)) and set up your own server:

```js
// @errors: 2307 7006
/// file: my-server.js
import { handler } from './build/handler.js';
import express from 'express';

const app = express();

// add a route that lives separately from the SvelteKit app
app.get('/healthcheck', (req, res) => {
	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');
});
```

> [!NOTE] When you use `handler.js` in a custom server, only the environment variables read by the handler itself take effect: `ORIGIN`, `PROTOCOL_HEADER`, `HOST_HEADER`, `PORT_HEADER`, `ADDRESS_HEADER`, `XFF_DEPTH`, and `BODY_SIZE_LIMIT`.
>
> The server-lifecycle variables (`PORT`, `HOST`, `SOCKET_PATH`, `SHUTDOWN_TIMEOUT`, `IDLE_TIMEOUT`, `KEEP_ALIVE_TIMEOUT`, `HEADERS_TIMEOUT`, `LISTEN_PID`, `LISTEN_FDS`) are only honored by the default `node build` server. Implement them yourself in a custom server if you need the same behavior — for example, the snippet above listens on a hardcoded `3000` regardless of `PORT`.
