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Cloudflare Workers

To deploy to Cloudflare Workers, use adapter-cloudflare-workers.

[!NOTE] Unless you have a specific reason to use adapter-cloudflare-workers, it's recommended that you use adapter-cloudflare instead. Both adapters have equivalent functionality, but Cloudflare Pages offers features like GitHub integration with automatic builds and deploys, preview deployments, instant rollback and so on.

Usage

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

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

export default {
	kit: {
		adapter: adapter({
			config: 'wrangler.toml',
			platformProxy: {
				configPath: 'wrangler.toml',
				environment: undefined,
				experimentalJsonConfig: false,
				persist: false
			}
		})
	}
};

Options

config

Path to your custom wrangler.toml or wrangler.json config file.

platformProxy

Preferences for the emulated platform.env local bindings. See the getPlatformProxy Wrangler API documentation for a full list of options.

Basic Configuration

This adapter expects to find a wrangler.toml/wrangler.json file in the project root. It should look something like this:

/// file: wrangler.toml
name = "<your-service-name>"
account_id = "<your-account-id>"

main = "./.cloudflare/worker.js"
site.bucket = "./.cloudflare/public"

build.command = "npm run build"

compatibility_date = "2021-11-12"
workers_dev = true

<your-service-name> can be anything. <your-account-id> can be found by logging into your Cloudflare dashboard and grabbing it from the end of the URL:

https://dash.cloudflare.com/<your-account-id>

[!NOTE] You should add the .cloudflare directory (or whichever directories you specified for main and site.bucket) to your .gitignore.

You will need to install wrangler and log in, if you haven't already:

npm i -g wrangler
wrangler login

Then, you can build your app and deploy it:

wrangler deploy

Custom config

If you would like to use a config file other than wrangler.toml you can specify so using the config option.

If you would like to enable Node.js compatibility, you can add "nodejs_compat" flag to wrangler.toml:

/// file: wrangler.toml
compatibility_flags = [ "nodejs_compat" ]

Runtime APIs

The env object contains your project's bindings, which consist of KV/DO namespaces, etc. It is passed to SvelteKit via the platform property, along with context, caches, and cf, meaning that you can access it in hooks and endpoints:

// @errors: 7031
export async function POST({ request, platform }) {
	const x = platform.env.YOUR_DURABLE_OBJECT_NAMESPACE.idFromName('x');
}

[!NOTE] SvelteKit's built-in $env module should be preferred for environment variables.

To make these types available to your app, install @cloudflare/workers-types and reference them in your src/app.d.ts:

/// file: src/app.d.ts
+++import { KVNamespace, DurableObjectNamespace } from '@cloudflare/workers-types';+++

declare global {
	namespace App {
		interface Platform {
+++			env?: {
				YOUR_KV_NAMESPACE: KVNamespace;
				YOUR_DURABLE_OBJECT_NAMESPACE: DurableObjectNamespace;
			};+++
		}
	}
}

export {};

Testing Locally

Cloudflare Workers specific values in the platform property are emulated during dev and preview modes. Local bindings are created based on the configuration in your wrangler.toml file and are used to populate platform.env during development and preview. Use the adapter config platformProxy option to change your preferences for the bindings.

For testing the build, you should use wrangler version 3. Once you have built your site, run wrangler dev.

Troubleshooting

Worker size limits

When deploying to workers, the server generated by SvelteKit is bundled into a single file. Wrangler will fail to publish your worker if it exceeds the size limits after minification. You're unlikely to hit this limit usually, but some large libraries can cause this to happen. In that case, you can try to reduce the size of your worker by only importing such libraries on the client side. See the FAQ for more information.

Accessing the file system

You can't use fs in Cloudflare Workers — you must prerender the routes in question.