Web apps

The platform builds the browser target of a Kotlin Multiplatform module and serves the result as a static site on its own host.

​

Set up the module

Declare a browser target and mark it executable. Wasm and JS both work:

kotlin {
    wasmJs {
        browser()
        binaries.executable()
    }
}

The platform runs wasmJsBrowserDistribution. If the module has no wasmJs browser target, it runs jsBrowserDistribution instead. Whatever the task writes to build/dist/<target>/productionExecutable is served as is, so index.html must be in that folder. The Compose Multiplatform wizard sets this up for you.

​

Hosts

• The primary web module is served at my-app-web.atoll.app.
• Other web modules are served at my-app-web--<module>.atoll.app.
• Previews get their own hosts, such as my-app--pr-42--web.atoll.app, so a pull request never changes production.

See Project structure for how module names become hosts.

​

Talking to your Ktor server

A web app usually needs the URL of its API. Set it as an env var for builds and read it in your Gradle build, for example with BuildKonfig or a generated source file:

atoll env set API_URL=https://my-app.atoll.app --no-runtime

See Environment variables. Changes take effect on the next build.

The web app and the server are on different hosts, also behind custom domains. Allow the web app’s origin in the server with Ktor’s CORS plugin.

​

Custom domains

Add a domain with --web to serve the primary web app on it:

atoll domains add www.example.com --web

See Custom domains.

​

Caching

index.html and other HTML files are always revalidated, so a new deployment shows up at once. Files with a content hash in their name, such as app.3f2a9c1b.js, are cached for a year. Everything else is cached and revalidated with its ETag.

​

Billing

Web apps are billed for the data they send, per GB. Builds count as build minutes. See Billing.