Google App Engine

Scalatra can run on Google App Engine Flexible Environment. You can use the provided Java 8 / Jetty 9 runtime, the provided Java 8 runtime (which would require you to write the server setup code yourself), or any external Docker image capable of running Java web applications.

Scalatra can run on Google App Engine Standard Java 8 runtime with some limitations, most notably no support for streaming responses and no support for Servlet 3+ async processing.

The old Java 7 runtime only supports Servlet API 2.5 and imposes even more restrictions, making it practically unusable with Scalatra.