Contracts

Apollo Studio contracts enable you to deliver different subsets of your graph to different consumers. Each contract filters specific portions of your graph's API schema into a different Studio variant:

Contracts filter schema definitions from your subgraph schemas based on @tag directives that you add:

type Product {
  id: ID!
  name: String!
  codename: String! @tag(name: "internal")
}

type Product {
  id: ID!
  name: String!
  # codename field is filtered out
}

In the above example, a contract excludes types and fields marked with the internal @tag.

What are contracts for?

You usually create a contract to support a contract gateway or contract documentation (or both).

Contract gateways

You can deploy a managed instance of your gateway that uses a contract schema. Developers who use this contract gateway can only execute GraphQL operations that the contract schema supports:

This enables you to hide experimental types and fields that are still in development, or to limit a particular audience's access to only the portions of your graph that they need.

Contract gateways can safely connect to the same subgraph instances as any other gateway, because they can only interact with data that's represented in the contract schema. This does not affect internal routing (hidden fields can still be used in a @requires selection set). Additionally, any @tag labels that are part of the source variant's supergraph schema are preserved in a contract supergraph schema.

Contract documentation

In Studio, each contract variant has its own README, schema reference, and Explorer. If you make a contract variant public, you can provide these resources to external client developers to help them interact with a specific portion of your graph (while omitting irrelevant types and fields).

Setup

1. Update your gateway and subgraphs

Before you create any contracts:

1. For Federation 2 contract variants, ensure that you're running gateway versions higher than 2.0.2. For Federation 1 contract variants, update your gateway's @apollo/gateway library to version 0.34.0 or later. Otherwise, you'll encounter runtime errors.
2. For Federation 2 contract variants, update your Apollo Server subgraphs to use 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.
   • @apollo/subgraph recently replaced @apollo/federation for Apollo Server instances acting as subgraphs. Symbol names are unchanged.
3. If you're still using the Apollo CLI to publish subgraph schemas (via apollo service:push), install the Rover CLI and begin using rover subgraph publish instead.

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

2. Enable variant support for @tag

A contract uses one of your graph's existing variants (called the source variant) to generate its contract schema. You need to enable the source variant's support for the @tag directive in Apollo Studio.

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

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

3. Add @tags

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 version of federation you're using:

1
directive @tag(name: String!) repeatable on
2
  | FIELD_DEFINITION
3
  | INTERFACE
4
  | OBJECT
5
  | UNION

1
extend schema
2
  @link(url: "https://specs.apollo.dev/federation/v2.0",
3
        import: ["@key", "@tag"])

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

1
extend schema
2
  @link(url: "https://specs.apollo.dev/federation/v2.0",
3
        import: ["@key", "@tag"])
4

5
type Query {
6
  topProducts: [Product!]! @tag(name: "partner")
7
}
8

9
# All fields of the Product object type automatically inherit
10
# the "partner" tag so we can avoid tagging them individually
11
type Product @key(fields: "upc") @tag(name: "partner") {
12
  upc: ID!
13
  name: String!
14
  description: String!
15
  # These fields also inherit the "partner" tag. You can
16
  # prevent access to them by defining an excludes filter in Studio
17
  internalId: ID! @tag(name: "internal")
18
  percentageMatch: Float! @tag(name: "experimental")
19
}

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

• The Product object type
• The Query.topProducts field (which returns a list of Products)
• 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 your source variant's supergraph schema is generated, that schema retains all of the @tags from your subgraph schemas.

Tagging rules

• In both Federation 1 and Federation 2, you can apply tags to the following in your schema:
  • Fields of object types (Federation 1 doesn't support tagging fields of interface types)
  • Definitions of object, interface, and union types
• In Federation 2 only, you can also apply tags to the following:
  • Definitions of custom scalar types
  • Enum types and their values
  • Input types and their fields
  • Fields of interface types
  • Arguments of fields, but not directive arguments at this time
• Tag names can include alphanumeric characters (a-z, A-Z, 0-9), along with hyphen (-) and forward slash (/).
• Each tag name cannot exceed 128 characters.
• Whenever you tag an object type definition, also tag every field that returns that type.
  • If you don't do this, a contract might exclude a type while including fields that return it. This produces an invalid contract schema.
• Whenever you tag an object or interface type, those tags propagate to the fields of that type.

Additional guidance is provided in Special cases.

4. Publish updated subgraph schemas

After you're done adding tags, update your source variant by publishing your updated subgraph schemas to Apollo Studio.

Now you're ready to create your first contract!

5. Create a contract

Once again open your source variant's Settings page and select the This Variant tab. This time, click Contracts:

Click Create Contract to open the following dialog:

Basic details

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

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

Then click Continue.

Contract filters

Next, you specify tag-based filters for your contract:

The dialog detects all tag names that are used in your source variant's schema, and it populates its dropdown lists with those names. You can add any number of tag names to each list.

Your contract will filter types and fields from its source variant according to the following rules:

• If the Included Tags list is empty, the contract schema includes each type and object/interface field unless it's tagged with an excluded tag.
• If the Included Tags list is non-empty, the contract schema excludes each union type and object/interface field unless it's tagged with an included tag.
  • Each object and interface type is included as long as at least one of its fields is included (unless the type is explicitly excluded)
  • The contract schema excludes a type or field if it's tagged with both an included tag and an excluded tag.

When you're done adding tag names, you can click Generate Preview to check the contract schema that your contract will generate. This enables you to make any necessary changes to your filters.

When you're ready, click Review.

Review and launch

You can now review all of the details of your contract:

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

6. Use your new contract variant

Congratulations! You've created a contract in Apollo Studio. You can now use your contract variant to provide a contract gateway or contract documentation to your users.

For example, you can complete the managed federation setup for a new gateway instance that uses your contract variant.

Federation 1 limitations

Contracts behave slightly differently depending on which version of Apollo Federation your graph uses (1 or 2). Most importantly, graphs that use Federation 1 cannot use @tags to exclude the following from a contract schema:

• Custom scalar types (default scalar types can never be excluded)
• Enum types or their values
• Input types or their fields
• Arguments of object fields or interface fields

Contracts and Federation 2

To create a contract variant that uses Federation 2, the contract's source variant must also use Federation 2.

Moving an existing contract to Federation 2

If a Federation 1 source variant already has one or more associated contracts, it isn't possible to move that variant or its contract variants to Federation 2. Instead, you need to delete and recreate your contract variants with the following steps:

1. Identify the source variant you want to move to Federation 2.
2. Save the details for each of that source variant's existing contract variants (most importantly each variant's associated filters).
3. Delete all of the source variant's existing contract variants.
4. Now that the source variant has no associated contracts, you can configure it to use Federation 2 composition (learn how).
5. Recreate your deleted contract variants, which will now use Federation 2 composition like the modified source variant.

Automatic updates

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

• Your contract's source variant successfully composes an updated API schema.
• You edit your contract.

This makes sure that your contract schema reflects the latest version of your source variant's schema, and that the correct types and fields are included and excluded.

Updates to your contract schema are automatically fetched by your managed contract gateways.

Editing a contract

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

Contract errors

Whenever Apollo Studio attempts to create or update your contract schema, it might encounter an error. Errors are identified by the step in the creation process where they occurred:

Special cases

• If a contract excludes every field of a particular object type, the entire type definition is excluded from the contract schema.

• If a contract excludes an object, interface, or union type, it must also exclude all schema fields that return that type. Otherwise, generation of the contract schema fails.

• If a contract has an includes filter, object and interface types without an included tag remain accessible (unlike other supported schema elements).

• If a contract excludes an object that implements an interface or is included in a union:

  • The contract is not required to exclude schema fields that return that interface or union.

  • However, if a subgraph resolves one of these fields by returning the excluded object, a runtime error occurs in the gateway and the operation fails.

• You cannot exclude any of the following from a contract schema:

  • Built-in scalars (Int, Float, etc.)
  • Built-in directives (@skip, @include, etc.)
  • Custom directives that are applied to type system locations (see the list)

• You can exclude object fields that are used in a computed field's @requires directive without causing runtime errors.

• Tags on objects and interface types (including tags on extension types) are inherited by all fields of that type.

• Tagging interface fields in Federation 1 is not supported. You can still make an interface field inaccessible by tagging the interface definition, or by ensuring that object fields that implement the interface field are removed.