The concept of a Serve Application, a data structure containing all information needed to deploy Serve on a Ray cluster, has surfaced during recent design discussions. This change introduces a formal Application data structure and refactors existing code to use it.
The REST API's schema default denies HTTP access to deployments when `route_prefix` is omitted. This doesn't match `@serve.deployment`'s behavior, which make `route_prefix` the deployment's name when omitted.
This change matches the schema's behavior to the decorator. When `route_prefix` is omitted from the config, the deployment's `route_prefix` defaults to its name. When the `route_prefix` is specified as `null`, the deployment won't have HTTP access.
This change also fixes a bug in Serve where when a deployment is updated from a non-`None` `route_prefix` to a `None` `route_prefix`, its `route_prefix` does not change. This bug meant that a deployment available over HTTP would continue to be available at the same route even when deployed again with `route_prefix=None`.
This change adds the GET, PUT, and DELETE commands for Serve’s REST API. The dashboard receives these commands and issues corresponding requests to the Serve controller.
