4. Schema checks in a supergraph
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Overview

The Listings team has some exciting updates ready to publish to the registry, but they need to be confident in these schema changes before publishing them to the production . Fortunately, there's an Apollo Studio feature to help with that: !

In this lesson, we will:

  • Learn about two types of (build checks and checks)
  • Understand how fit into the overall process of updating a
  • Learn about the process in Apollo Studio

In this lesson, we'll focus mainly on the high-level overview of the process. The next lesson will dive more into the details of how to run each check.

What are schema checks?

Schema checks are a set of predefined tests that help identify potential failures caused by schema updates. They check for issues like incompatibilities between or breaking existing client . With , we can ensure that our schema changes won't cause issues when we deploy to production.

There are two types of : build checks and checks.

Build checks

Build checks validate that a 's schema changes can still compose successfully with other in the .

Build checks are only available for federated , because non-federated graphs aren't composed into a .

Illustration of subgraph characters being checked for composition

For example, if a new type is added to one , a build check determines whether that addition is compatible with the rest of the subgraphs in the . If it isn't, we need to investigate the error and fix it. We'll take a look at common errors later on in the course.

Operation checks

checks validate that a schema's changes won't break any operations that existing clients send to the . Unlike build checks, operation checks are available for non-federated in addition to federated graphs.

Illustration of Studio checking a schema against existing operations

For example, let's say a web client regularly sends a to retrieve data for its homepage. If a schema change involves adding a required to a in that query, it might break that client's existing ! An operation check helps us guard against this potential failure, listing out the affected operations and allowing the team to address them. We'll also take a look at an example of this later on in the course.

How to run schema checks

There are two main ways to run . We can run schema checks locally, using the . We can also integrate schema checks into our CI pipelines to run automatically (which lets us do things like block merging any pull request that fails schema checks). We'll get to the pipeline stuff later in the course. For now, we'll focus on running schema checks locally.

To perform a schema check for a , we use the 's rover subgraph check command. This runs a build check first, then an check, and finally outputs the results in the command line. It also reports the results to Apollo Studio, so you can view them from your 's Checks page. We'll see in action in the next lesson.

Schema checks in the supergraph story

Let's revisit our story and zoom in to where occur and what happens when they fail, pass, or are actively overridden.

After making changes to a (whether that's adding, removing, or updating definitions), we first want to run locally using . For a , a build check happens first, then checks run.

First, validates that a 's schema changes can still compose successfully with the other in the . By default, this check runs against the current of the , but we can also select any graph variant already registered in Studio.

If the build check succeeds, runs an check immediately after. This validates that the schema's changes won't break any operations that existing clients send to the .

Illustration using Rover for a local build check, variants in the registry

If either check fails, provides a link to the Studio Checks page that contains more information about what went wrong.

If all the checks are successful, we can go ahead and follow the same process as before: we'll use to publish the to the registry.

Illustration of schema checks fitting into the story of a supergraph. See description in paragraphs above for full outline of the process.

While we're on the subject of publishing schema changes, let's take a moment to touch on a useful feature of Apollo Studio: a launch.

Launch process

By publishing to the schema registry, we've triggered a launch in Apollo Studio.

A represents the complete process of making schema updates to any of a . You'll already be familiar with some of the steps in a launch (we covered them in Voyage I), but there are a few new steps thrown in the mix to include our handy !

A starts with Studio attempting to compose the . If it fails, we'll see an error and the process stops there. Otherwise, a is produced. The supergraph schema is provided to Uplink and our will fetch the latest schema.

We've successfully completed our schema updates to the !

Illustration of launches and how they fit into the story of a supergraph. See description in paragraphs above for full outline of the process.

And that's what and the process look like in our .

Practice

Schema checks
There are two types of schema checks. Checks that validate if a subgraph's schema changes can still 
 
 successfully with other subgraph schemas are called 
 
, which are available for 
 
. Checks that validate a schema's changes against existing 
 
 sent by clients are called 
 
, which are available for 
 
.

Drag items from this box to the blanks above

  • query checks

  • combination checks

  • compose

  • federated graphs

  • combine

  • operation checks

  • operations

  • non-federated graphs

  • supergraph checks

  • both federated and non-federated graphs

  • build checks

Which of the following statements about launches in Apollo Studio are true?

Key takeaways

  • help identify potential failures caused by schema updates before they can cause issues in production. There are two types of schema checks: build checks and checks.
  • Build checks validate that a 's schema changes can still compose successfully with other . These checks are only available for federated graphs.
  • checks validate that a schema's changes won't break any operations that existing clients are sending to the . These checks are available for both federated and non-federated graphs.
  • To run a schema check, we use the rover subgraph check command.
  • A represents the complete process of making schema updates to any of a . It's triggered by a being published to the schema registry.

Up next

In the next three lessons, we'll see how work in our development workflow and how they can be automated in the CI/CD process.

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