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Hosting Updates on Your Servers

Normally, when over-the-air (OTA) updates are enabled, your app will fetch updates comprising JavaScript bundles and assets from Expo’s CDN. However, there will be situations when you will want to host your JS bundles and assets on your own servers. For example, OTA updates are slow or unusable in countries that have blocked Expo’s CDN providers on AWS and Google Cloud. In these cases, you can host your updates on your own servers to better suit your use cases.
For simplicity, the rest of this article will refer to hosting an update for the Android platform, but you could swap out Android for iOS at any point and everything would still be true.

Exporting the update

First, you’ll need to export all the static files of your update so they can be served from your CDN. To do this, run expo export --public-url <server-endpoint> in your project directory and it will output all your app’s static files to a directory named dist. In this guide, we will use https://expo.github.io/self-hosting-example as our example server endpoint. Asset and bundle files are named by the MD5 hash of their content. Your output directory should look something like this now:
├── android-index.json
├── ios-index.json
├── assets
│   └── 1eccbc4c41d49fd81840aef3eaabe862
└── bundles
      ├── android-01ee6e3ab3e8c16a4d926c91808d5320.js
      └── ios-ee8206cc754d3f7aa9123b7f909d94ea.js

Once you've exported your update's static files, you can host the contents on your own server. For example, in your dist output directory, an easy way to host your own files is to push the contents to Github. You can enable Github Pages to make your app available at a base URL like https://username.github.io/project-name. To host your files on Github, you'd do something like this:
# run this from your project directory
expo export --public-url https://expo.github.io/self-hosting-example

# commit output directory contents to your repo
cd dist
git init && git remote add origin git@github.com:expo/self-hosting-example.git
git add * && git commit -m "Update my app with this JS bundle"
git push origin master
To setup a QR code to view your hosted update, or if you want to host your files locally, follow the instructions below in the 'Loading QR Code/URL in Development' section.

On some hosting services such as AWS and Firebase, you'll need to explicitly set the header "Content-Type" of JavaScript files as "application/javascript" so that OTA Updates work correctly. Otherwise Updates.checkForUpdateAsync() will fail with the error "Failed to fetch new update".
Here's an example of firebase.json configuration, with a deploy target named "native".
  "hosting": [
      "target": "native",
      "public": "dist",
+      "headers": [
+        {
+          "source": "**/*.js",
+          "headers": [
+            {
+              "key": "Content-Type",
+              "value": "application/javascript"
+            }
+          ]
# export your app locally
expo export --public-url https://my-app-native.firebaseapp.com/

# deploy the app to firebase
firebase deploy --only hosting:native -m "Deploy my app"`

In order to configure your standalone binary to pull OTA updates from your server, you’ll need to define the URL where you will host your index.json file. Pass the URL to your hosted index.json file to the expo build command.
For iOS builds, run the following commands from your terminal: expo build:ios --public-url <path-to-ios-index.json>, where the public-url option will be something like https://expo.github.io/self-hosting-example/ios-index.json
For Android builds, run the following commands from your terminal: expo build:android --public-url <path-to-android-index.json>, where the public-url option will be something like https://expo.github.io/self-hosting-example/android-index.json

You can also load an update hosted on your own servers as a QR code/URL into the Expo mobile client for development purposes.

The URI you’ll use to convert to QR code will be deeplinked using the exps/exp protocol. Both exps and exp deeplink into the mobile app and perform a request using HTTPS and HTTP respectively. You can create your own QR code using an online QR code generator from the input URI.

URI: exps://expo.github.io/self-hosting-example/android-index.json
QR code: Generate the URI from a website like https://www.qr-code-generator.com/

Run expo export in dev mode and then start a simple HTTP server in your output directory:
# Find your local IP address with `ipconfig getifaddr en0`
# export static app files
expo export --public-url http://`ipconfig getifaddr en0`:8000 --dev

# cd into your output directory
cd dist

# run a simple http server from output directory
python -m SimpleHTTPServer 8000
URI: exp://192.xxx.xxx.xxx:8000/android-index.json (find your local IP with a command like ipconfig getifaddr en0)
QR code: Generate a QR code using your URI from a website like https://www.qr-code-generator.com/

If you are loading in your update into a development client by passing in a URL string, you will need to pass in an URL pointing to your JSON manifest file.
Here is an example URL from a remote server: https://expo.github.io/self-hosting-example/android-index.json
Here is an example URL from localhost: http://localhost:8000/android-index.json

When Expo CLI bundles your update, minification is always enabled. In order to see the original source code of your update for debugging purposes, you can generate source maps. Here is an example workflow:
  1. Run expo export --dump-sourcemap --public-url <your-url>. This will also export your bundle sourcemaps in the bundles directory.
  2. A debug.html file will also be created at the root of your output directory.
  3. In Chrome, open up debug.html and navigate to the Source tab. In the left tab there should be a resource explorer with a red folder containing the reconstructed source code from your bundle.
Debugging Source Code

As new Expo SDK versions are released, you may want to serve multiple versions of your app from your server endpoint. For example, if you first released your app with SDK 29 and later upgraded to SDK 30, you'd want users with your old standalone binary to receive the SDK 29 version, and those with the new standalone binary to receive the SDK 30 version. In order to do this, you can run expo export with some merge flags to combine previously exported updates into a single multiversion update which you can serve from your servers.
Here is an example workflow:
  1. Release your update with previous Expo SDKs. For example, when you released SDK 29, you can run expo export --output-dir sdk29 --public-url <your-public-url>. This exports the current version of the update (SDK 29) to a directory named sdk29.
  2. Update your app and include previous Expo SDK versions. For example, if you've previously released SDK 28 and 29 versions of your app, you can include them when you release an SDK 30 version by running expo export --merge-src-dir sdk29 --merge-src-dir sdk28 --public-url <your-url>. Alternatively, you could also compress and host the directories and run expo export --merge-src-url https://examplesite.com/sdk29.tar.gz --merge-src-url https://examplesite.com/sdk28.tar.gz --public-url <your-url>. This creates a multiversion update in the dist output directory. The asset and bundle folders contain everything that the source directories had, and the index.json file contains an array of the individual index.json files found in the source directories.

By default, all assets are hosted from an assets path resolving from your public-url (e.g. https://expo.github.io/self-hosting-example/assets). You can override this behavior in the assetUrlOverride field of your android-index.json. All relative URL's will be resolved from the public-url.

Most of the fields in the index.json files are the same as in app.json. Here are some fields that are notable in index.json:
  • revisionId, commitTime, publishedTime: These fields are generated by expo export and used to determine whether or not an OTA update should occur.
  • bundleUrl: This points to the path where the app's bundles are hosted. They are also used to determined whether or not an OTA update should occur.
  • slug: This should not be changed. Your app is namespaced by slug, and changing this field will result in undefined behavior in the Expo SDK components such as Filesystem.
  • assetUrlOverride: The path which assets are hosted from. It is by default ./assets, which is resolved relative to the base public-url value you initially passed in.