Creating and using contracts

Create contracts

Prerequisites

Update your router and subgraphs

Before you create any contracts:

1. If you're using Apollo Server:

   • For Federation 2 contract variants, update your Apollo Server subgraphs to version 2.0.0 or later of the @apollo/subgraph library.
   • For Federation 1 contract variants, update @apollo/subgraph to version 0.1.1 or later.

2. If you're using the @apollo/gateway library instead of the Apollo Router:

   • For Federation 2 contract variants, update your gateway's @apollo/gateway library to version 2.0.2 or later.
   • For Federation 1 contract variants, update your gateway's @apollo/gateway library to version 0.34.0 or later.

Older versions of the above libraries and tools don't fully support the required @tag directive.

(Fed1 only) Enable variant support for @tag

A contract uses one of your graph's existing variants (called the source variant) to generate its contract schema. If your source variant uses Federation 1, you need to enable its support for the @tag directive in GraphOS Studio:

1. Open the Settings page for the variant you want to use as your source variant, then select the This Variant tab:

   

2. In the Build Configuration section, click Edit Configuration and enable support for @tag.

1. Add @tags to subgraph schemas

With contracts, you apply the @tag directive to types and fields in your subgraph schemas to indicate whether to include or exclude them from your contract schema.

Before you can add @tags, you need to define the directive in your subgraph schema. The way you do this depends on which federation version you're using:

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directive @tag(
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  name: String!
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) repeatable on FIELD_DEFINITION | INTERFACE | OBJECT | UNION

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extend schema
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  @link(
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    url: "https://specs.apollo.dev/federation/v2.0"
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    import: ["@key", "@tag"]
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  )

For example, let's take a look at this Federation 2 subgraph schema:

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extend schema
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  @link(
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    url: "https://specs.apollo.dev/federation/v2.0"
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    import: ["@key", "@tag"]
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  )
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type Query {
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  topProducts: [Product!]! @tag(name: "partner")
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}
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# All fields of the Product object type automatically inherit
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# the "partner" tag so we can avoid tagging them individually
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type Product @key(fields: "upc") @tag(name: "partner") {
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  upc: ID!
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  name: String!
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  description: String!
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  internalId: ID! @tag(name: "internal")
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  percentageMatch: Float! @tag(name: "experimental")
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}

This schema applies the @tag directive to the following locations:

• The Query.topProducts field (which returns a list of Products)
• The Product object type
• Two fields of Product (internalId and percentageMatch)

Each @tag has a string name. You tag types and fields with the same name if they should be included or excluded as a group by a particular contract.

Whenever GraphOS composes your source variant's supergraph schema, that schema retains all the @tags from your subgraph schemas. Composition removes some other directives by default. Learn more.

2. Publish updated subgraph schemas

After you've added tags, update your source variant by publishing your updated subgraph schemas to GraphOS.

3. Create a contract

1. Open your source variant's Settings page and select the This Variant tab. Open Contracts in the left nav:

   

2. Click Create Contract to open the following dialog:

   

3. In the first step of the dialog, provide the following:

   • A name for your new contract variant
   • The source variant to use

   ⓘ NOTE

   You can't change these values after the contract is created.

4. Click Continue.

5. Specify tag-based filters for your contract:

   

   • The dialog detects all tag names used in your source variant's schema and populates the Excluded Tags and Included Tags dropdown lists with those names. You can add any number of tag names to each list.

   • You can also add tag names not yet present in your source variant's schema. If you later add tags with that name, the contract honors them.

6. When you're finished adding tag names, click Generate Preview. Studio attempts to generate a contract schema based on the filters you provided and displays the result. After you generate the preview, click Review to continue to the next step.

   

7. Review all the details of your contract:

   

8. If everything looks right, click Create. This kicks off the generation of your contract variant and its initial contract schema as a launch.

Using contract variants

You can use your contract variants to provide contract routers or contract documentation to your users. For example, you can complete the managed federation setup for a new router instance that uses your contract variant.

Automatic updates

Apollo automatically updates your contract schema whenever any of the following occurs:

• GraphOS successfully composes an updated supergraph schema for the contract's source variant.
• You edit your contract.

These automatic updates ensure that your contract schema reflects your source variant's latest version and that the correct types and fields are included and excluded.

Your managed contract routers automatically fetched updates to your contract schema.

Edit contracts

After you create a contract, you can edit its lists of included and excluded tags:

1. From the Contracts list in your graph's Settings page, click Edit Contract where shown:

   

   This opens a dialog similar to the one you used to create the contract. Make any required changes.

2. If you change the contract's included or excluded tags, GraphOS automatically runs contract checks to determine whether those changes will affect any clients using your contract variant. The result of these checks appears in the Review Schema step of the contract edit dialog:

   

3. The dialog shows Contract Updated once the update is complete.

Run contract checks

If you run schema checks in GraphOS Studio (which we recommend for all graphs), those checks include contract checks for any variant that acts as a source variant for contracts. Contract checks help your team identify when proposed changes to a source variant will negatively affect one or more downstream contracts.

When you run schema checks on a source variant, contract checks execute alongside the other checks for that variant (composition checks and operation checks).

Contract checks rely on the supergraph schema generated by composition, so they don't execute if composition checks fail.

Contract checks do the following for each of a source variant's associated contracts:

1. Use the source variant's proposed supergraph schema (validated by composition checks) to generate and validate an updated contract schema.
2. Run operation checks against the updated contract schema.

On your graph's Checks page in Studio, contract checks appear as Downstream:

You can click the Downstream item in the Tasks column to view a summary of all contract checks that ran and click a particular check to view more details:

Failing contract checks

Unlike other types of checks, failing contract checks don't cause their associated schema checks workflow to fail by default. This means that the rover subgraph check command doesn't return an error state that would prevent a CI task from merging or deploying changes to the source variant.

If you want failing contract checks to fail your entire checks workflow, you can set the blocking downstream variants configuration for your source variant. If contract checks fail for any of these specified contract variants, the source variant's checks workflow does fail.

To set blocking downstream variants:

1. Open your source variant's Checks page and select the This Variant tab.

2. Click Configuration and scroll down to the Blocking Downstream Variants section:

   

3. Select each contract variant that should be a blocking downstream variant.

From now on, whenever schema checks run for your source variant, those checks fail if contract checks fail for any blocking downstream variant.