Rover supergraph commands

A supergraph (also called a federated graph) is a graph composed of multiple subgraphs:

Rover commands that interact with supergraphs begin with rover supergraph. These commands primarily deal with supergraph schemas, which adhere to the core schema specification.

Composing a supergraph schema

You can use the supergraph compose command to compose a supergraph schema based on a supergraph configuration file, like so:

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rover supergraph compose --config ./supergraph.yaml

You can also pass config via stdin:

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cat ./supergraph.yaml | rover supergraph compose --config -

Configuration

The supergraph configuration file (often referred to as supergraph.yaml) includes configuration options for each of your subgraphs. The following example file configures a supergraph with two subgraphs, films and people:

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subgraphs:
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  films:
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    routing_url: https://films.example.com
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    schema:
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      file: ./films.graphql
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  people:
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    routing_url: https://people.example.com
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    schema:
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      file: ./people.graphql

In the above example, The YAML file specifies each subgraph's public-facing URL (routing_url), along with the path to its schema (schema.file).

It's also possible to pull subgraphs from various sources and specify them in the YAML file. For example, here is a configuration that specifies schema using Apollo Registry refs (subgraph, graphref) and subgraph introspection (subgraph_url):

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subgraphs:
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  films:
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    routing_url: https://films.example.com
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    schema:
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      file: ./films.graphql
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  people:
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    routing_url: https://example.com/people
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    schema:
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      subgraph_url: https://example.com/people
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  actors:
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    routing_url: https://localhost:4005
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    schema:
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      graphref: mygraph@current
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      subgraph: actors

Using with Federation 2

To use Rover with a Federation 2 supergraph, you need to add federation_version: 2 to your YAML configuration file.

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federation_version: 2
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subgraphs:
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  films:
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    routing_url: https://films.example.com
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    schema:
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      file: ./films.graphql

The first time you run rover supergraph compose with Federation 2 on a particular machine, you're prompted 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).

Output format

By default, rover supergraph compose outputs a supergraph schema document to stdout. You provide this artifact to @apollo/gateway or the 🦀 Apollo Router on startup.

You can also save the output to a local .graphql file like so:

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# Creates prod-schema.graphql or overwrites if it already exists
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rover supergraph compose --config ./supergraph.yaml > prod-schema.graphql

Gateway compatibility

Apollo Gateway fails to start up if it's provided with a supergraph schema that it doesn't support. To ensure compatibility, we recommend that you test launching your gateway in a CI pipeline with the supergraph schema it will ultimately use in production.

Federation 1 vs. Federation 2

The rover supergraph compose command generates a supergraph schema via composition. For Federation 1, this algorithm was implemented in the @apollo/federation package. For Federation 2, this algorithm is implemented in the @apollo/composition package.

rover supergraph compose supports composing subgraphs with both Federation 1 and Federation 2. By default, Rover uses Federation 2 composition if and only if at least one of your subgraph schemas contains the @link directive. Otherwise, it uses Federation 1.

When Apollo releases new versions of composition for Federation 1 or Federation 2, Rover downloads the new package to your machine. Rover then uses the new composition package to compose your subgraphs. Our aim is to release only backward-compatible changes across major versions moving forward. If composition breaks from one version to the next, please submit an issue, and follow the instructions for pinning composition to a known good version.

If you set federation_version: 1 or federation_version: 2, you can run rover supergraph compose with the --skip-update flag to prevent Rover from downloading newer composition versions. Rover instead uses the latest major version that you've downloaded to your machine. This can be helpful if you're on a slow network.

If any subgraph schema contains the @link directive and you've specified federation_version: 1, you either need to revert that subgraph to a Federation 1 schema or move your graph to Federation 2.

Earlier Rover versions

Prior to Rover v0.5.0, rover supergraph compose shipped with exactly one version of composition that was compatible with Federation 1. This function was sourced from the @apollo/federation JavaScript package. Therefore, it was important to keep track of your Rover version and your Gateway version and keep them in sync according to the following compatibility table.

Fetching a supergraph schema from Apollo Studio

You can use Rover to fetch the supergraph schema of any federated Studio graph and variant it has access to. Run the supergraph fetch command, like so:

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rover supergraph fetch my-graph@my-variant

The argument my-graph@my-variant in the example above specifies the ID of the Studio graph you're fetching from, along with which variant you're fetching.