• Quickstart
• Configuration Overview
• Details
  • firebase.json Configurations
  • Adapter Configurations
• Cloud Function
  • Firebase Emulator local Testing
  • Deployment
  • Caveats
• Cloud Run
  • Local Testing
  • Deployment
  • Caveats
• Function vs Run
• Non-Goals
• FAQ
• Caveats
• Contributing

In your standard SvelteKit project:

• npm i -D svelte-adapter-firebase

• add adapter to svelte.config.cjs:

  const firebaseAdapter = require("svelte-adapter-firebase");
  
  /** @type {import('@sveltejs/kit').Config} */
  module.exports = {
    kit: {
      adapter: firebaseAdapter(),
      target: "#svelte",
    },
  };

• npm run build

• Follow further instructions output by the adapter to prepare for deployment.

This adapter reads your firebase.json to determine if the Firebase Hosting site is using Cloud Functions or Cloud Run and outputs the server pieces accordingly. Static assets are output to the public directory for the Hosting site config.

Please read the docs carefully!

Adapter options:

• hostingSite
  • required when firebase.json.hosting is an array (contains many site configurations)
  • default: no default value
• sourceRewriteMatch
  • used to lookup the rewrite rule used for SSR
  • default: **
• firebaseJson
  • path to your firebase.json, relative from where svelte build is called
  • default: ./firebase.json
• cloudRunBuildDir
  • output dir of Cloud Run service, relative from your svelte app
  • default: ./.${run.serviceId} where run.serviceId is pulled from the firebase.json rewrite rule

Quickstart outlines the steps most commonly used with a single SvelteKit app. Here we go into the details of each configuration and how it interacts with the firebase.json config.

The 3 step process is:

1. select Hosting config from firebase.json. If more than one site match against hostingSite
2. output static assets to the directory in the public field
3. identify the rewrite rule for SSR to determine Cloud Function or Cloud Run output. The rewrite rule is determined by a lookup of the rewrites.source against sourceRewriteMatch

Due to the relaxed rules of firebase.json we can have many valid configs. At a minimum, one or more Hosting sites is required with an associated Functions config if a Cloud Function rewrite is used. These are the combintations:

{
  "hosting": {
    "public": "<someDir>",
    "rewrites": [
      {
        "source": "**",
        "function": "<functionName>"
      }
    ]
  },
  "functions": {
    "source": "<anotherDir>"
  }
}

{
  "hosting": [
    {
      "site": "blog",
      "public": "<someDir>",
      "rewrites": [
        {
          "source": "**",
          "function": "<functionName>"
        }
      ]
    },
    {
      // another site config
    }
  ],
  "functions": {
    "source": "<anotherDir>"
  }
}

const firebaseAdapter = require("svelte-adapter-firebase");

/** @type {import('@sveltejs/kit').Config} */
module.exports = {
  kit: {
    adapter: firebaseAdapter({ hostingSite: "blog" }),
    target: "#svelte",
  },
};

{
  "hosting": {
    "public": "<someDir>",
    "rewrites": [
      {
        "source": "**",
        "run": {
          "serviceId": "<cloudRunServiceId>"
        }
      }
    ]
  }
}

{
  "hosting": [
    {
      "site": "blog",
      "public": "<someDir>",
      "rewrites": [
        {
          "source": "**",
          "run": {
            "serviceId": "<cloudRunServiceId>"
          }
        }
      ]
    },
    {
      // another site config
    }
  ]
}

const firebaseAdapter = require("svelte-adapter-firebase");

/** @type {import('@sveltejs/kit').Config} */
module.exports = {
  kit: {
    adapter: firebaseAdapter({ hostingSite: "blog" }),
    target: "#svelte",
  },
};

Detailed examples of the adapter configuration options.

// firebase.json
{
  "hosting": [
    {
      "site": "blog",
      "public": "<someDir>",
      "rewrites": [
        {
          "source": "**",
          "run": {
            "serviceId": "<cloudRunServiceId>"
          }
        }
      ]
    },
    {
      "site": "adminPanel",
      "public": "<anotherDir>"
    }
  ]
}

const firebaseAdapter = require("svelte-adapter-firebase");

/** @type {import('@sveltejs/kit').Config} */
module.exports = {
  kit: {
    adapter: firebaseAdapter({ hostingSite: "blog" }),
    target: "#svelte",
  },
};

// firebase.json
{
  "hosting": {
    "public": "<someDir>",
    "rewrites": [
      {
        "source": "/blog/**",
        "run": {
          "serviceId": "<cloudRunServiceId>"
        }
      }
    ]
  }
}

const firebaseAdapter = require("svelte-adapter-firebase");

/** @type {import('@sveltejs/kit').Config} */
module.exports = {
  kit: {
    adapter: firebaseAdapter({ sourceRewriteMatch: "/blog/**" }),
    target: "#svelte",
  },
};

.gitignore
firebase.json
app/                    <-- svelte build run in this dir
	package.json
	svelte.config.cjs
	src/
anotherApp/
	index.html
	index.css
functions/
	package.json
	index.js

const firebaseAdapter = require("svelte-adapter-firebase");

/** @type {import('@sveltejs/kit').Config} */
module.exports = {
  kit: {
    adapter: firebaseAdapter({ firebaseJson: "../firebase.json" }),
    target: "#svelte",
  },
};

// firebase.json
{
  "hosting": {
    "public": "public",
    "rewrites": [
      {
        "source": "**",
        "run": {
          "serviceId": "mySiteSSR"
        }
      }
    ]
  }
}

.mySiteSSR/         <--- Cloud Run service code
public/             <--- Hosting static assets
firebase.json
package.json
svelte.config.cjs
src/
	app.html
	routes/
		index.svelte
functions/
	package.json
	index.js

const firebaseAdapter = require("svelte-adapter-firebase");

/** @type {import('@sveltejs/kit').Config} */
module.exports = {
  kit: {
    adapter: firebaseAdapter({ cloudRunBuildDir: ".special/ssr/output/dir" }),
    target: "#svelte",
  },
};

With this firebase.json and functions/ dir in a standard SvelteKit app structure and default svelte-adapter-firebase config:

// firebase.json
{
  "hosting": {
    "public": "myApp",
    "rewrites": [
      {
        "source": "**",
        "function": "ssrServer"
      }
    ],
    "predeploy": ["npm run build"]
  },
  "functions": {
    "source": "functions"
  }
}

firebase.json ("public": "myApp")
package.json
svelte.config.cjs
src/
	app.html
	routes/
		index.svelte
functions/
	package.json ("main": "index.js")
	index.js
	sveltekit/		<-- Server assets
myApp/				<-- Static assets to go to Firebase Hosting CDN

The firebase.json functions.source dir is used to find functions/package.json whose main field is used to find the Cloud Function build dir. This is used as the server asset output dir.

firebase.json ("public": "myApp")
package.json
svelte.config.cjs
src/
	app.html
	routes/
		index.svelte
functions/
	package.json ("main": "lib/index.js")
	index.ts
	lib/
		index.js
		sveltekit/	<-- Server assets output to functions/lib
myApp/				<-- Static assets to go to Firebase Hosting CDN

firebase.json ("site": "myCoolSite","public": "myApp")
package.json
svelte.config.cjs
src/
	app.html
	routes/
		index.svelte
functions/
	package.json
	index.js
	myCoolSite/		<-- Server assets
myApp/				<-- Static assets to go to Firebase Hosting CDN

The final piece is to write the actual Cloud Function source code to reference the output server assets. The code is printed during svelte build and should be placed in your index.js or index.ts manually.

This is a flexible solution that allows integrating with other Cloud Functions in your project. You can edit the provided code as you see fit. The import/require of the generated code will not change unless you change the firebase.json.hosting.site or package.json.main fields, so you shouldn't need to update this code after adding it.

Test your production build locally before pushing to git or deploying!

• build your app: svelte-kit build
• install Function dependencies: pnpm install --prefix functions
• start the emulator: firebase emulators:start

firebase deploy, that is all.

As package.json gains dependencies for your Svelte app you may need to copy some of these to functions/package.json depending on the server-side functionality and how SvelteKit bundles your dependencies. ℹ️ This should be re-evaluated again in the future as it changes depending on SvelteKit and may not exist as a caveat in 1.0.0 release.

With this firebase.json a standard SvelteKit app structure and default svelte-adapter-firebase config:

// firebase.json
{
  "hosting": {
    "public": "<someDir>",
    "rewrites": [
      {
        "source": "**",
        "run": {
          "serviceId": "mySiteSSR"
        }
      }
    ]
  }
}

will result in this output:

.mySiteSSR/         <--- This contains the Cloud Run service code
firebase.json
package.json
svelte.config.cjs
src/
	app.html
	routes/
		index.svelte
functions/
	package.json
	index.js

See the official Hosting/Cloud Run docs here for more setup information (enabling required APIs etc).

For those interested, we support Cloud Run with the same JS code as Cloud Functions, via the NodeJS Functions Framework and reliance on the Node.js 14 Buildpacks, which is what essentially powers Cloud Functions.

Cloud Run cannot be tested locally with the Firebase Emulator. However, you can still build and run it locally with gcloud cli:

gcloud beta code dev --builder

This will build the container using the Google Node 14 buildpack image, run the image locally, and rebuild the image on code changes. For more details, see - https://cloud.google.com/run/docs/testing/local#cloud-sdk_

When you route to the hosted image you should be able to navigate your Cloud Run app but your CDN hosted resources (css, images, etc) will not load properly. This can be used as a sanity check

gcloud CLI is required to build & deploy Cloud Run services. The recommended build & deploy command for Cloud Run will be output when the adapter is run.

gcloud beta run deploy ${serviceId} --platform managed --region ${region} --source ${serverOutputDir} --allow-unauthenticated

Notably, this command builds and deploys your container, which is traditionally a two step process for container runtimes. You can orchestrate your deployment however you wish. Feel free to modify the command with any other Cloud Run features you may want to use, like increasing the concurrency or setting min_instances

This deploy command uses Cloud Build and the aforementioned Buildpacks and Functions Framework.

⚠️ Each build of your app will require firebase deploy --only hosting alongside your Cloud Run deployment as your CDN content will need to be updated as the filename hashes of static resources is rewritten on each svelte-kit build

• testing of a Cloud Run service with Firebase Hosting CDN and other backend features (PubSub/Cloud Functions) will require a full deployment to a Firebase project. The suggestion is a dev project per engineer and manual deployments to each env to test. No environment per PR here.

Choice is a good thing, hopefully this comparison table helps you decide which compute environment is best for your application:

Cloud Functions seems do be a better default.

Write Cloud Function code directly into .js file instead of printing in console.

Firebase Cloud Functions have a long history of people configuring their index files completely differently, some even generating them from directories. Accommodating these would be a headache. Instead, all we look for is a match against this string, ${name} =, where name is your Cloud Functions name. We may make this configurable to a specific file in future.

Additionally, this allows for users to customise their Firebase Cloud Function API like runWith() options for memory/CPU and VPC/Ingress/Egress configuration settings, without complex support for options in the adapter. This keeps the Function config where it should, close to the executing code.

Handle the deployment of the app to Firebase.

Firebase apps consist of many different services with the CLI providing optional deployments. We do not want to dictate full deployments with your frontend nor perform partial deployments if it does not fit your app. The only option then is to leave it to you 🎉

Custom Docker images

We support Cloud Run with the same JS code as Cloud Functions, via the NodeJS Functions Framework and reliance on the Node14 Buildpacks, which is what essentially powers Cloud Functions. Diverging from this would make supporting Cloud Run more difficult. The idea behind the support is to allow usage of Cloud Run features, for example, min_instances and concurrent requests which both reduce cold starts (if that matters to you, use the CDN!)

We are open to discussion on this topic, but it was not a goal when setting out to build this adapter (consider the cost/benefit).

Why is the Cloud Function code output to the terminal for me to add manually instead of being written to functions/index.js?

See non-goals Write Cloud Function code directly into .js file instead of printing in console.

Firebase libs in SvelteKit routes

This adapter does not try to solve the issue of using Firebase libraries in SvelteKit routes. These routes are compiled by the SvelteKit pipeline and there are many issues as ESM support in Firebase libs is not released and won't be for a long time.

Using Firebase libs in SvelteKit endpoints/routes may have been resolved with sveltejs/kit#490, however this does not mean the output is compatible with the Cloud Function runtime (investigation pending) and therefore compatible with svelte-adapter-firebase. Our recommendation is to prefer using Firebase Cloud Functions for API routes over SvelteKit routes.

Cold Starts

Depends on your application load. Typically, Cloud Functions will require more instances to handle the same number of requests as each Cloud Run as each CR instance can handle up to 250 (default maximum at the time of writing). Though in my experience, bumping the memory/cpu configuration dramatically reduces the response times.

Since the purpose of using this adapter is to leverage the Firebase Hosting CDN, you should consider improving the user experience with targetted caching/TTLs.

If cold starts are still an issue for your application, Cloud Run has support for min_instances which will keep x number of instances warm. This incurs additional costs. See the Cloud Run documentation for more.

• Firebase Hosting Preview Channels currently lacks first-party support for SSR applications. This adapter doesn't attempt to remedy this issue and doesn't produce a different SSR Function/Run for preview channel deployments.
• ⚠️ while you can specify the region for both, Cloud Run in firebase.json and Cloud Functions in runWith({}) config, us-central1 is the only valid region for Firebase Hosting rewrites, other regions will error. The official warning about this can be found in these docs.
• 1.0.0 will not be published until the SvelteKit Adapter API is declared stable and SvelteKit is released for general use.

Contributions of any kind welcome, just follow the guidelines!

Short version:

git clone https://github.com/jthegedus/svelte-adapter-firebase.git
asdf install
pnpm i

• Cloud Function validation code linked in utils.js is from two different sources which indicates that it is being validated by firebase-tools in two separate places. PR a fix there.