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Rover conventions


These are conventions for all Rover commands.

Terminology

Graph / Subgraph / Supergraph

Rover provides commands for interacting with federated subgraphs and supergraphs, along with commands for interacting with a monolithic (non-federated) graph.

A supergraph is the composition of multiple subgraphs in a federated architecture:

Supergraph (A + B + C)
Subgraph A
Subgraph B
Subgraph C

When working on a federated graph, you'll run most Rover commands on a particular subgraph (using a subgraph command), rather than on the whole composed supergraph. The supergraph commands are useful when working with supergraph schemas.

Graph refs

Rover uses graph refs to refer to a particular variant of a particular graph in Apollo Studio. A graph ref is a string with the following format:

graph_id@variant_name

For example: docs-example-graph@staging

All Rover commands that interact with the Apollo graph registry require a graph ref as their first positional argument. If you're using the default variant (current), you don't need to include the @variant_name portion of the graph ref (although it's recommended for clarity).

I/O

Using stdout

Rover commands print to stdout in a predictable, portable format. This enables output to be used elsewhere (such as in another CLI, or as input to another Rover command). To help maintain this predictability, Rover prints logs to stderr instead of stdout.

To redirect Rover's output to a location other than your terminal, you can use the pipe | or output redirect > operators.

Pipe |

Use the pipe operator to pass the stdout of one command directly to the stdin of another, like so:

rover graph introspect http://localhost:4000 | pbcopy

In this example, the output of the introspect command is piped to pbcopy, a MacOS command that copies a value to the clipboard. Certain Rover commands also accept values from stdin, as explained in Using stdin.

Output redirect >

Use the output redirect operator to write the stdout of a command to a file, like so:

rover graph fetch my-graph@prod > schema.graphql

In this example, the schema returned by graph fetch is written to the file schema.graphql. If this file already exists, it's overwritten. Otherwise, it's created.

Using stdin

Rover commands that take a file path as an option can instead accept input from stdin. To do so, pass - as the argument for the file path:

rover graph introspect http://localhost:4000 | rover graph check my-graph --schema -

In this example, the schema returned by graph introspect is then passed as the --schema option to graph check.

Currently, --schema is the only Rover option that accepts a file path.

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