The Rover dev command

A subgraph is a graph that contributes to the composition of a federated supergraph:

You can use Rover to start a local router that can query across one or more running GraphQL APIs (i.e., subgraphs) through one endpoint. As you add, edit, and remove subgraphs, Rover automatically composes their separate schemas into a unified supergraph schema that the router reloads and serves.

Think plug-n-play USB devices but with your GraphQL APIs!

Creating a federated session

Starting the session

Before using rover dev, you need at least one running GraphQL API (subgraph). You'll need the URL the GraphQL API is serving, along with the location of its schema in your filesystem.

Here's an example rover dev command that provides a locally running subgraph:

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rover dev --name products --schema ./products.graphql --url http://localhost:4000

This starts the rover dev session, which watches ./products.graphql for changes to the schema. It also starts up a local Apollo Router instance at its default endpoint (http://localhost:3000). Finally, the session listens for other rover dev processes that include different subgraph schemas.

Stopping the session

If you stop the first rover dev session (by pressing CTRL+C), it shuts down the local router instance. It also detaches and shuts down any secondary rover dev processes.

Attaching additional subgraphs to a session

To add a new GraphQL API (i.e., subgraph) to a session, run rover dev in a new terminal with the necessary arguments for that new subgraph. If a session is already running, Rover automatically attaches subsequent rover dev processes to that existing session.

When you add a new subgraph to a session, Rover handles recomposing the supergraph schema and printing the build result in the outputs of both the primary process and the attached process.

Triggering recomposition on subgraph changes

Each rover dev process is responsible for monitoring any changes to its subgraph schema.

Via filesystem update (recommended)

If you pass the --schema <PATH> argument, rover dev watches that schema file for changes and reports any updates to the main rover dev process if a schema's contents change.

Via introspection

If you don't pass the --schema <PATH> argument, rover dev introspects the URL specified by the --url <SUBGRAPH_URL> argument once every second. The command prefers to use the same query as rover subgraph introspect but it falls back to rover graph introspect if your GraphQL API doesn't support introspecting federated SDL. If this is the case, directives are stripped from the subgraph schema.

Stopping an attached process

If you stop an attached rover dev process (by pressing CTRL+C), the supergraph will recompose its schema without the removed subgraph and reload the router.

Health check

By deafult, the health check endpoint is disabled in rover dev. You can enable it again by enabling it in a router configuration YAML file and passing it to rover dev via the --router-config argument described in the following section.

Advanced configuration

To configure advanced router functionality like CORS settings or header passthrough for subgraphs, you can pass a valid router configuration YAML file to rover dev via the --router-config <ROUTER_CONFIG_PATH> argument.

Note that only the main rover dev process uses this router configuration file when starting the router. If you specify a different listen address with supergraph.listen, all other rover dev processes need to pass the same values to --supergraph-port and --supergraph-address, and/or pass the same router configuration file path via --router-config.

Federation 2 ELv2 license

The first time you use Federation 2 composition on a particular machine, Rover prompts you to accept the terms and conditions of the ELv2 license. On future invocations, Rover remembers that you already accepted the license and doesn't prompt you again (even if you update Rover).

The ELv2-licensed plugins, supergraph (built from this source) and router (built from this source) are installed to ~/.rover/bin if you installed with the curl | sh installer, and to ./node_modules/.bin/ if you installed with npm.

Versioning

By default, rover dev will select a recent version of the router and composition to use for you. You can override these by setting the environment variables APOLLO_ROVER_DEV_COMPOSITION_VERSION=2.0.0 and/or APOLLO_ROVER_DEV_ROUTER_VERSION=1.0.0. By default, rover dev will always use a composition library with a major version of 2, and a router with a major version of 1. If you already have the plugins installed, you can pass --skip-update to rover dev in order to keep the plugins at the same version.