API Reference: @apollo/gateway

Apollo Gateway API reference

This API reference documents the exports from the @apollo/gateway package.

`class ApolloGateway`

The core class of Apollo Server's federated gateway implementation. For an example of using ApolloGateway, see The gateway.

Methods

`constructor`

Returns an initialized ApolloGateway instance, which you can then pass as the gateway configuration option to the ApolloServer constructor, like so:

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const server = new ApolloServer({
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  gateway: new ApolloGateway({
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    serviceList: [
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      // ...
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    ]
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  }),
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});

Takes an options object as a parameter. Supported fields of this object are described below.

Examples

Providing a `serviceList` and headers to authorize introspection

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const gateway = new ApolloGateway({
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  serviceList: [
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    { name: 'products', url: 'https://products-service.dev/graphql' },
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    { name: 'reviews', url: 'https://reviews-service.dev/graphql' }
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  ],
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  introspectionHeaders: {
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    Authorization: 'Bearer abc123'
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  }
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});

Configuring the subgraph fetcher

If you provide a buildService function to the constructor of ApolloGateway, the function is called once for each of your graph's subgraphs. This function can return a RemoteGraphQLDataSource with a custom fetcher, which is then used for all communication with subgraphs:

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const gateway = new ApolloGateway({
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  buildService({ url, name }) {
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    return new (class extends RemoteGraphQLDataSource {
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      fetcher = require('make-fetch-happen').defaults({
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        onRetry() {
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          console.log('We will retry!')
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        },
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      });
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    })({
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      url,
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      name,
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    });
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  }
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});

Configuring the managed federation fetcher

This only configures the fetcher that your gateway uses to fetch managed federation configuration from Apollo.

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const gateway = new ApolloGateway({
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  fetcher: require('make-fetch-happen').defaults({
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    onRetry() {
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      console.log('We will retry!')
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    },
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  }),
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});

Options

Name / Type	Description
`supergraphSdl` `string \| SupergraphSdlHook \| SupergraphManager`	You provide your supergraph schema to the gateway with this option. You can provide it as a `string`, via a `SupergraphSdlHook`, or via a `SupergraphManager`. When `supergraphSdl` is a `string`: A supergraph schema (generated with the Rover CLI) that's composed from your subgraph schemas. The supergraph schema includes directives that specify routing information for each subgraph. When `supergraphSdl` is a `SupergraphSdlHook`: This is an `async` function that returns an object containing a `supergraphSdl` string as well as a `cleanup` function. The hook accepts an object containing the following properties: `update`: A function that updates the supergraph schema `healthCheck`: A function that issues a health check against the subgraphs `getDataSource`: A function that gets a data source for a particular subgraph from the gateway When `supergraphSdl` is a `SupergraphManager`: An object containing an `initialize` property. `initialize` is an `async` function of the `SupergraphSdlHook` type described directly above. If you are using managed federation, do not provide this field. *If you aren't* using managed federation,** either this field or `serviceList` is required. Do not provide both.
`serviceList` `Array<ServiceEndpointDefinition>`	This option is deprecated in favor of the drop-in replacement, `IntrospectAndCompose`. An array of objects that each specify the `name` and `url` of one subgraph in your federated graph. On startup, the gateway uses this array to obtain your subgraph schemas via introspection and compose a supergraph schema. You can specify any string value for the `name` field, which is used for identifying the subgraph in log output and error messages, and for reporting metrics to Apollo Studio. If you are using managed federation, do not provide this field. *If you aren't* using managed federation,** either this field or `supergraphSdl` is required. Do not provide both.
`introspectionHeaders` `Object \| (service: ServiceEndpointDefinition) => (Promise<Object> \| Object)`	This option is deprecated in favor of the drop-in replacement, `IntrospectAndCompose`. An object (or an optionally async function returning an object) that contains the names and values of HTTP headers that the gateway includes only when making introspection requests to your subgraphs. If you are using managed federation, do not provide this field. If you define a `buildService` function, specify these headers in that function instead of providing this option. This ensures that your `buildService` function doesn't inadvertently overwrite the values of any headers you provide here.
`debug` `Boolean`	If `true`, enables development mode helpers and logs messages of all severity levels (`debug` through `error`). If `false`, only `warn`- and `error`-level messages are logged. The default value is `false`.
`logger` `Logger`	An object to use for logging in place of `console`. If provided, this object must implement all methods of the `Logger` interface. If you provide this value, the gateway automatically logs all messages of all severity levels (`debug` through `error`), regardless of whether the `debug` option is set to `true`. It is the responsibility of the logger to determine how to handle logged messages of each level. This logger is automatically added to the `GraphQLRequestContext` object that's passed to all Apollo Server plugin functions.
`fetcher` `Fetcher`	Specifies which Fetch API implementation to use with managed federation when fetching configuration from Apollo. By default, the gateway uses the default configuration of `make-fetch-happen`. You can specify another valid implementation (such as `node-fetch`) by setting this field's value to `require('node-fetch')`. As shown in the example above, you can also provide `make-fetch-happen` to this option if you want to override the library's default configuration.
`serviceHealthCheck` `Boolean`	If `true`, the gateway sends a small query (`{ __typename }`) to all subgraphs on gateway startup. It also does the same on each live schema update if you're using managed federation. On startup, the gateway throws an error if any of these requests fail. On schema update, the gateway does not roll over to the new schema or graph configuration if any of these requests fail. The gateway retries the requests at each polling interval until they succeed. The default value is `false`.
`uplinkEndpoints` `Array<string>`	A list of Apollo Uplink URLs the gateway uses to poll for its managed configuration. For details and defaults, see Apollo Uplink. Provide this field only if you are using managed federation and your use case specifically requires it (this is uncommon).
`uplinkMaxRetries` `number`	The maximum number of times the gateway retries a failed poll request to Apollo Uplink, cycling through its list of `uplinkEndpoints`. The default value is to try each of your uplinkEndpoints three times (i.e., 5 retries with the default list of two endpoints). Provide this field only if you are using managed federation.
`fallbackPollIntervalInMs` (managed mode only) `number`	Specify this option as a fallback if Uplink fails to provide a polling interval. This will also take effect if `fallbackPollIntervalInMs` is greater than the Uplink defined interval.
`buildService` `Function`	Define this function to customize your gateway's data transport to some or all of your subgraphs. This customization can include using a protocol besides HTTP. For details, see The `buildService` function.

The `buildService` function

If you provide this function, the gateway calls it once for each subgraph. The function must return an object that implements the GraphQLDataSource interface, such as an instance of RemoteGraphQLDataSource or a subclass of it.

The example below demonstrates adding an x-user-id HTTP header to every request the gateway sends to a subgraph:

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class AuthenticatedDataSource extends RemoteGraphQLDataSource {
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  willSendRequest({ request, context }) {
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    request.http.headers.set('x-user-id', context.userId);
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  }
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}
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const gateway = new ApolloGateway({
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  // ...other options...
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  buildService({ name, url }) {
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    return new AuthenticatedDataSource({ url });
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  },
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});

Experimental options

These options are experimental. They might be removed or change at any time, even within a patch release.

Name / Type	Description
`experimental_approximateQueryPlanStoreMiB` `number`	Sets the approximate size (in MiB) of the gateway's query plan store. This cache is used to save query plans for reuse on subsequent queries that resolve to a previously observed `queryHash` (the SHA-256 of the incoming operation). The default value is `30`, which is usually sufficient unless the server processes a large number of unique operations.

`serviceHealthCheck`

When called, the gateway sends a small query ({ __typename }) to each subgraph to verify that they're all responsive. This function throws on failure and returns a Promise to be awaited.

Parameters

Name / Type	Description
`serviceMap` `Object` (`DataSourceMap`)	If provided, the gateway sends health check requests to only the data sources included in the map. By default, the gateway uses `this.serviceMap` (i.e., it sends health check requests to all known subgraphs).

`class RemoteGraphQLDataSource`

Represents a connection between your federated gateway and one of your subgraphs.

You can customize this connection by extending this class and overriding its willSendRequest and/or didReceiveResponse methods:

Override willSendRequest to modify your gateway's requests to the subgraph before they're sent.
Override didReceiveResponse to modify the subgraph's responses before the gateway passes them along to the requesting client.

These methods are described in detail below.

Methods

`constructor`

Returns an initialized RemoteGraphQLDataSource instance:

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const productsDataSource = new RemoteGraphQLDataSource({
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  url: 'https://products-service.dev/graphql'
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});

Takes an options object as a parameter. Supported fields of this object are described below.

Options

Name / Type	Description
`url` `String`	Required. The subgraph's URL for sending fetch requests via HTTP.
`apq` `Boolean`	If `true`, the gateway attempts to use automated persisted queries (APQ) when sending queries to this subgraph. APQ can dramatically reduce the size of most requests sent over the network, especially for more complex queries. The subgraph must also enable support for APQ for the gateway to use this feature (Apollo Server enables APQ by default).

`willSendRequest`

Override this method in a subclass to modify each outgoing fetch request before it's sent to the subgraph:

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// Adds an `x-user-id` header to each outgoing fetch request
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class AuthenticatedDataSource extends RemoteGraphQLDataSource({
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  willSendRequest({ request, context }) {
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    request.http.headers.set('x-user-id', context.userId);
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  }
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});

This method takes a requestContext object that contains both the original unmodified request and the current context.

`didReceiveResponse`

Override this method in a subclass to customize the gateway's behavior after it completes a fetch to the subgraph, but before it sends a response to the requesting client:

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class CookieDataSource extends RemoteGraphQLDataSource {
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  didReceiveResponse({ response, request, context }) {
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    const cookie = request.http.headers.get('Cookie');
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    if (cookie) {
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      context.responseCookies.push(cookie);
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    }
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    // Return the response, even when unchanged.
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    return response;
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  }
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}

This method takes a requestContext object that contains:

The subgraph's response
The gateway's request to the subgraph
The current operation's context

This enables you to modify any combination of the operation's context and the response of the fetch.

The http property of the request and response objects contains additional HTTP-specific properties, such as headers.

This method must return an object that matches the structure of a GraphQLResponse. If no modifications are necessary, return the original response.

`didEncounterError`

Override this method in a subclass to customize the gateway's behavior after it encounters an error while communicating with the subgraph or while parsing its response (e.g., if the response is not well-formed JSON).

If you don't override this method, the default implementation throws the error, like so:

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class MyDataSource extends RemoteGraphQLDataSource {
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  didEncounterError(error, fetchRequest, fetchResponse, context) {
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    throw error;
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  }
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}

Note that if you don't throw error (or a different Error) in this method, error is thrown immediately after this method returns.

This method takes the following positional parameters:

Name / Type	Description
`error` `Error`	The error that occurred during communication.
`fetchRequest` `Request`	The details of the `fetch` request sent to the subgraph.
`fetchResponse` `Response`	The details of the `fetch` response sent by the subgraph.
`context` `TContext`	The `context` argument passed between the GraphQL operation's resolvers.

`class IntrospectAndCompose`

IntrospectAndCompose is a development tool for fetching and composing subgraph SDL into a supergraph for your gateway. Given a list of subgraphs and their URLs, IntrospectAndCompose will issue queries for their SDL, compose them into a supergraph, and provide that supergraph to the gateway. It can also be configured to update via polling and perform subgraph health checks to ensure that supergraphs are updated safely. IntrospectAndCompose implements the SupergraphManager interface and is passed in to ApolloGateway's supergraphSdl constructor option.

IntrospectAndCompose is the drop-in replacement for serviceList.

Methods

`constructor`

Returns an initialized IntrospectAndCompose instance, which you can then pass to the supergraphSdl configuration option of the ApolloGateway constructor, like so:

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const server = new ApolloServer({
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  gateway: new ApolloGateway({
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    supergraphSdl: new IntrospectAndCompose({
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      subgraphs: [
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        // ...
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      ],
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    }),
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  }),
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});

Takes an options object as a parameter. Supported properties of this object are described below.

Examples

Providing a `subgraphs` list and headers to authorize introspection

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const gateway = new ApolloGateway({
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  supergraphSdl: new IntrospectAndCompose({
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    subgraphs: [
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      { name: 'products', url: 'https://products-service.dev/graphql' },
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      { name: 'reviews', url: 'https://reviews-service.dev/graphql' },
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    ],
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    introspectionHeaders: {
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      Authorization: 'Bearer abc123'
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    },
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  }),
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});

Configuring the subgraph fetcher

IntrospectAndCompose uses the data sources constructed by ApolloGateway. To customize the gateway's data sources, you can provide a buildService function to the ApolloGateway constructor. In the example below, IntrospectAndCompose makes authenticated requests to the subgraphs via the AuthenticatedDataSources that we construct in the gateway's buildService function.

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const gateway = new ApolloGateway({
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  buildService({ name, url }) {
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    return new AuthenticatedDataSource({ url });
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  },
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  supergraphSdl: new IntrospectAndCompose({
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    subgraphs: [
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      { name: 'products', url: 'https://products-service.dev/graphql' },
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      { name: 'reviews', url: 'https://reviews-service.dev/graphql' },
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    ],
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  }),
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});

Options

Name / Type	Description
`subgraphs` `Array<ServiceEndpointDefinition>`	An array of objects that each specify the `name` and `url` of one subgraph in your federated graph. On startup, `IntrospectAndCompose` uses this array to obtain your subgraph schemas via introspection and compose a supergraph schema. The `name` field is a string that should be treated as a subgraph's unique identifier. It is used for query planning, logging, and reporting metrics to Apollo Studio. For Studio users, subgraph names must: Begin with a letter (capital or lowercase) Include only letters, numbers, underscores (_), and hyphens (-) Have a maximum of 64 characters
`introspectionHeaders` `Object \| (service: ServiceEndpointDefinition) => (Promise<Object> \| Object)`	An object (or an optionally async function returning an object)that contains the names and values of HTTP headers that the gateway includes only when making introspection requests to your subgraphs. If you define a `buildService` function in your `ApolloGateway` config, specify these headers in that function instead of providing this option. This ensures that your `buildService` function doesn't inadvertently overwrite the values of any headers you provide here.
`pollIntervalInMs` `number`	Specify this option to enable supergraph updates via subgraph polling. `IntrospectAndCompose` polls each subgraph at the given interval.
`subgraphHealthCheck` `boolean`	This option applies only to subgraphs that are configured for polling via the `pollIntervalInMs` option. If `true`, the gateway performs a health check on each subgraph before performing a supergraph update. Errors during health checks will result in skipping the supergraph update, but polling will continue. The health check is a simple GraphQL query (`query __ApolloServiceHealthCheck__ { __typename }`) to ensure that subgraphs are reachable and can successfully respond to GraphQL requests. This option is the `IntrospectAndCompose` equivalent of `ApolloGateway`'s `serviceHealthCheck` option. If you are using `IntrospectAndCompose`, enabling `serviceHealthCheck` on your `ApolloGateway` instance has no effect.
`logger` `Logger`	An object to use for logging in place of `console`. If provided, this object must implement all methods of the `Logger` interface. `IntrospectAndCompose` doesn't share the same logger as the `ApolloGateway` it's configured with. In most cases, you probably want to pass the same logger to both `ApolloGateway` and `IntrospectAndCompose`.

Edit on GitHub

@apollo/subgraph

Subgraph specification